Windows 7 32-bit might work, BUT you would have to upgrade the RAM/memory to AT LEAST 1GB - maxing it out at 2GB would be better.
Windows 8 would require a processor that supports NX/Execute Disable ... not all P4's do.
64-bit would require a processor that supports 64-bit ... not all P4's do. Your system does not support enough memory to make this a worthwhile upgrade (64-bit).
All in all, if you already have a valid, unused, RETAIL license for Windows 7, this machine might run it ok, but I probably wouldn't waste any money buying it for this system.
You might start by running the Windows 7 Upgrade Advisor to see if you will run into any problems with Windows 7:
The system was never tested with any of these Operating System. Hence the drivers are also unavailable in Dell Support Site. However, Windows 7 might work as the flash has said. It also has the capability of installing the generic drivers but for few drivers you would have to look into the manufacturer website of the hardware component. For more details, see Windows 7 system requirements.
I would also like to say that Windows 8 requires UEFI Bios which the Dimension 5150 does not have. Hence Windows 8 would be unsupported on this system. For more details, see Dell Computer Support for Windows 8 Upgrade.
Hope this helps!
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This system works great with Windows 7 32 bit.
As mentioned above you should have at least 1 GB of RAM installed. RAM is pretty cheap so I recommend installing a minimum of 2 GB but preferably 4 GB.
As you are in the UK you may obtain RAM from these 2 places. Crucial is in general recommended for Dell systems but I have had many a good purchase with Offtek also which is slightly cheaper for DDR2 RAM:
They are sold in kits of 2 GB (2×1 GB modules) so to get the 4 GB of RAM you require 2 kits. You machine has 4 memory slots.
The crucial website also has a system scanner and will inform you what slots you have free and how much memory you currently have installed.
For the Windows 7 installation see Windows Reinstallation Guide/A Clean install of Windows 7: http://philipyip.wordpress.com/dell-community-forums/
I would advise installing Windows 7 using a .iso from Digital River (ignore Step 2 the system locked preinstallation as it won't work or apply to your system). Install this without a product key and you can evaluate Windows 7 for 30 days to see whether you like how your system runs before deciding whether you want to buy the license or not.
You could also try installation of the Windows 8.1 Consumer preview 32 bit also mentioned in Windows Reinstallation Guide/A Clean install of Windows 8. I personally prefer Windows 7 to Windows 8.1 and prefer that to Windows 8 but each user has their own preferences.
If you feel up to it you could of course evaluate both to see what one you like best before purchasing.
Driver wise likely everything will natively work with Windows 7 32 Bit with Service Pack 1 but for best performance install the below drivers.
For Windows 8.1 32 bit ignore the OS updates category and Dell System Software. In fact I wouldn't bother installing any additional drivers on Windows 8.1 it should have all the drivers inbuilt. Ensure you have the latest BIOS revision before installing Windows 8.1 however.
* Not required if the installation media includes the Service Pack.
** requires internet connection
* Requires Internet Connection.
Intel 82945G [Variant A]*
ATI AutoUpdate [Variant B]*
* This system may have a dedicated graphics card installed, check the Card slots at the bottom/back of the system. If no graphics card is there use the onboard Intel 82945G video.
* This system may have a Creative SoundBlaster installed, check the Card slots at the bottom/back of the system. If no soundcard is there use the onboard Sigmatel Audio driver or use no driver (if you are satisfied with the sound quality).