First off, can't say I blame Dell for not wanting to support Windows 10 on these laptops.  What would you do if component manufacturers weren't creating drivers?  I wouldn't support Windows 10 either.  But, never tell me something can't be done, I'll do it anyway.  I have Windows 10 installed and running, no problems, everything working.

Unless noted, all drivers are native Windows 10 64 bit.  Some drivers had to come from my desktop motherboard that uses the H77 chipset.

When downloading drivers, I group them in folders named after the OS the driver is meant for, then a folder named after the component the driver is for. 

Bios Update
I updated my BIOS.  May not be needed, but having the latest bios sometimes solves problems with new OSes.  I leave this one up to you.

ATI Radeon HD 7970M
http://support.amd.com/en-us/download/mobile?os=Windows+10+-+64
Never download video drivers from Dell for Nvidia or Ati cards, Dell falls waaaayyyyy behind on driver updates.

Intel Rapid Storage
For installing Windows 10:
http://www.dell.com/support/home/us/en/19/Drivers/DriversDetails?driverId=GF4K5&fileId=3154961274&osCode=W764&productCode=alienware-m17x-r4&languageCode=EN&categoryId=SA
Once Windows 10 is installed:
http://www.dell.com/support/home/us/en/19/Drivers/DriversDetails?driverId=JRG1T&fileId=3287490389&osCode=WB64A&productCode=alienware-m17x-r4&languageCode=EN&categoryId=SA

Realtek Card Reader
http://www.realtek.com.tw/Downloads/downloadsView.aspx?Langid=1&PNid=15&PFid=25&Level=4&Conn=3&DownTypeID=3&GetDown=false
A universal driver, might work for other realtek card readers.

Alienware On Screen Display
http://www.dell.com/support/home/us/en/19/Drivers/DriversDetails?driverId=N9PMP&fileId=3287517716&osCode=WB64A&productCode=alienware-m17x-r4&languageCode=EN&categoryId=AP

SoundBlaster Recon 3D
No need for drivers, Windows 10 has drivers.

Dell Command Center
http://www.dell.com/support/home/us/en/19/Drivers/DriversDetails?driverId=2J54X&fileId=3485313456&osCode=WT64A&productCode=alienware-17-r3&languageCode=EN&categoryId=AP
Might be the Windows 10 replacement for Alienware Command Center, but doesn't work.  Noting this one in case someone wants to try, don't waste your time.

Alienware Command Center
http://www.dell.com/support/home/us/en/19/Drivers/DriversDetails?driverId=X6VV1&fileId=3148080684&osCode=W864&productCode=alienware-m18x-r2&languageCode=EN&categoryId=AP
C++ 2010 Runtime x64: http://www.microsoft.com/en-us/download/confirmation.aspx?id=13523
Install the C++ runtime and add .NET Framework 3.5 before installing Alienware Command Center.  .NET Framework can be found by going to "Apps & features" in System Settings, then "Manage Optional Features".

Intel HM77 Chipset
A Windows 10 driver was not found on Intel's website.  I used my deskptop motherbaord's driver.
http://dlcdnet.asus.com/pub/ASUS/misc/utils/Intel_Chipset_Win10_V10117.zip  DO NOT use AsusSetup.exe!

Intel Management Engine
For a windows 10 version, I used my desktop motherboard drivers.
http://dlcdnet.asus.com/pub/ASUS/misc/utils/MEI1-5_Win10_VER11001157.zip

Dell Wireless 380 Bluetooth
http://www.dell.com/support/home/us/en/04/Drivers/DriversDetails?driverId=XGR27

Synaptic Touchpad
http://www.dell.com/support/home/us/en/19/Drivers/DriversDetails?driverId=R0Y00&fileId=3485314402&osCode=WT64A&productCode=alienware-17-r3&languageCode=EN&categoryId=IN  

Intel Centrino WiMAX 6250
Intel has not released a Windows 10 driver, may never release a windows 10 driver.  The windows 7 driver is the only one that installs.  Seems to be working fine for me.
http://www.dell.com/support/home/us/en/19/Drivers/DriversDetails?driverId=M4HVV&fileId=2947394894&osCode=W764&productCode=alienware-m17x-r4&languageCode=EN&categoryId=NI

Intel USB 3.0 eXtensible Host Controller
No need for drivers.  Microsoft has USB 3.0 drivers included in Windows 10.

Airplane Mode Switcher
http://www.dell.com/support/home/us/en/19/Drivers/DriversDetails?driverId=7YJ68&fileId=3485314063&osCode=WT64A&productCode=alienware-17-r3&languageCode=EN&categoryId=NI

Intel HD Display Driver
Had to go with my desktop motherboard driver to get a Windows 10 compatible version.
http://dlcdnet.asus.com/pub/ASUS/misc/vga/Intel_Graphics_Win10_VER1018104252.zip

Accelerometer
http://www.dell.com/support/home/us/en/19/Drivers/DriversDetails?driverId=5T449&fileId=3126802194&osCode=W864&productCode=alienware-m17x-r4&languageCode=EN&categoryId=UT

Clean Install the Upgrade
I don't have time to do a step by step, at least these pointers should get you in the right direction.

When installing, Windows 10 will not detect any hard drive.  Make sure to extract the Windows 7 Intel Rapid Storage drivers to a place the Windows 10 installer will find.  I put them on the USB drive I used for installing the OS.  When asked for extra drivers, go to the "f6flpy-x64" folder for the rapid storage drivers.  The only way to get the folder is to extract the contents on the Dell installer.  Once Windows 10 is installed, don't forget to install the Window 8.1 version of the driver.

If you want to do a clean install using the free upgrade, install the upgrade on top of the current OS.  Make sure Windows 10 is activated by going to "System", which can be found by right clicking "This PC" then "Properties" in Windows Explorer.  Do the clean install, skipping the serial key entry windows when they come up.  Windows 10 will automatically activate once installation is done.  DO NOT forget to upgrade first, otherwise you'll have to install your current os again.  Some drivers may need Windows Update to run in order to install them, make sure to update.

Once done with a clean install, I used CloneZilla to create a backup of the install.

That should cover everything.  Hope this helps.  Don't fault Dell for component manufacturers not creating compatible drivers.