How big harddisk can an dell dimension 4600 have installed?

DRIVES Up to 120 gig are fine.  IDE drives are hard to find but you can use a KINGWIN ADP-06  Adapter with SATA DRIVES 80 to 250 gigs which are easy to find.  48 bit LBA requires the latest bios.

https://www.amazon.com/Kingwin-SATA-Bridge-Board-ADP-06/dp/B002SZDOM6/

https://www.amazon.com/Western-Digital-WD800JD-75MSA3-7200RPM-WD800JD75MSA3/dp/B003GBCNQO/

http://www.dell.com/support/home/us/en/19/drivers/driversdetails?c=us&l=en&s=dhs&driverid=R84099

https://downloads.dell.com/bios/D4600A12.EXE

When i purchase the computer there 200 GB IDE HDD on want to install Win 7 Home Premium, the CPU is an 32 bit CUP.IM not in america but in Europe. Would it be okay to installed 200 or 250 GB GB SATA HDD? if so which 250 GB SATA HDD schould i install?

What do need a converter  for the pc is already have the option of SATA Drive?

Do in really need an KINGWIN ADP-06  Adapter if want install a 250 GB SATA drive on the pc?

Is it hard vo installed the newest Bios i know i have Bios version A6 on the PC?

I have done it myself many years ago but i dont remember how i did it?

The 4600 is very very flaky using the onboard sata interface.  Not booting, crashing,etc.  This is another reason why there were sooo many bios updates for this model.  ANY IDE drive must be set cable select and the DVD rom may not boot from a windows 7 DVD without FIRMWARE updates to the Drive.   Honestly the 4600 is too old and too slow to work well.   You would be better off finding a GX620 mini tower or better.  They often are available WITH WINDOWS for the cost of windows alone and will be 5 to 25 times faster than the 4600.

This is also an area where the Kingwin Adapter helps.  You buy a new inexpensive SATA DVD and use with the Kingwin Adapter and Viola the windows 7 dvd actually is readable and boots.

Any drive larger than 120 gigs may only be seen as 120 gigs without 48 bit LBA bios which came out in 2005.   The Kingwin adapter has nothing to do with the drive size.

I believe it was an issue windows that killed my harddisk . I have had no problem with Runing Ubuntu and now Ubuntu MATE 16.04 LTS 32 bit on my 4600 dimension for years. The problems started first when i try install windows 7 on the pc.

WINDOWS 7 installs fine on IDE Drives or SATA Drives with the KINGWIN adapter on the IDE interface.  USING Sata requires F6 Mass storage drivers.