consolegamer :
I'm considering building a PC based around a Haswell/Broadwell processor, and I have an old copy of Windows XP enterprise lying around. Needless to say, I'm not crazy about spending $100 on Windows 8 if I can use XP, so my question is this: would a Haswell/Broadwell mobo be compatible with Windows XP? I have a $100 mobo budget if that helps.
The simple and easiest answer is yes and no.
Intel dropped SATA AHCI XP driver support for Haswell. However there are unofficial modded drivers out that might allow you to do it which I have not tested.
Also for Intel HD Graphics there is no XP driver support for the HD 4200 integrated GPU and higher which usually come with Haswell CPUs. The Intel HD 4000 found on Ivy Bridge CPUs was the cut off for XP driver support.
[Sandy Bridge and Ivy Bridge method]
The easiest and best way to get XP running on a modern motherboard is to go get a Z77 motherboard. I can guarantee you the Z77 has SATA AHCI drivers and Intel HD graphic drivers for XP. I've built several passive HTPCs using this chipset and have had no problems.
I've installed XP, Vista, and 7 in a MultiOS boot system and I love the flexibility. It is better to install XP first then newer OS after or XP will overwrite the bootloader for the newer OS.
The reason Intel dropped support for XP is because Microsoft stopped supporting it on April 8th, 2014.
Insert the XP CD and set it to boot off this drive first.
Install the SATA AHCI drivers either by using an external 1.44MB floppy disk with the copied drivers to the root directory of the A:.
Quickly hit F6 when it asks if you have any 3rd party drivers to install.
Video
http://www.youtube.com/watch?v=6oDT40ewh90
Alternative method:
Use nLite to slipstream the SATA AHCI drivers into a hard drive folder and then burn this to a CD.
To install from a hard drive folder it must be done from DOS which may be beyond the skill set of most people using computers today.
After XP has finished installing, install the latest Intel HD graphics driver for XP.
Reboot.
Now you should have video and if you are using HDMI you will also have audio.
Install all other drivers for other devices such as the Chipset, onboard audio, network and wireless, et cetera.
[Haswell / Broadwell method]
Now, if you want to really try to get it running on Haswell, you will face a few obstacles.
You have to locate a modded SATA AHCI driver for your Chipset which aren't officially from Intel.
Or if your motherboard BIOS has a setting for IDE compatibility mode you might be able to install it without problems.
You have to get a discrete graphics card that has XP driver support.
Next you will have to get make sure your onboard audio has XP drivers or if not you will need to get a dedicated sound card to get sound.
[Decision Time]
Now if you've decided the method that works best is to stick with my suggestion and get the older Z77 Ivy Bridge.
These are getting harder to find but here is one still with abundant supply on Amazon.
Gigabyte LGA 1155 DDR3 1600 Intel Z77 HDMI SATA 6Gb/s USB 3.0 ATX Intel Motherboard with UEFI BIOS GA-Z77-HD3
http://www.amazon.com/Gigabyte-1155-Intel-Motherboard-GA-Z77-HD3/dp/B00APZXYGM/ref=sr_1_7?s=pc&ie=UTF8&qid=1406391318&sr=1-7&keywords=z77+motherboard:
$105 Free Shipping and tax where applicable.
If you want a real basic HTPC system pair this motherboard with this best bang for the buck low end CPU.
It is a Celeron but it is quite powerful. I've underclocked this to 1.8GHz and run off a CPU core voltage of 0.60V to save energy. Contains the Intel HD 1000 integrated graphics with Windows XP driver support.
Intel Celeron G1620 2.70GHz LGA-1155 Processor BX80637G1620
http://www.amazon.com/Intel-Celeron-LGA-1155-Processor-BX80637G1620/dp/B00B4BJY7E
$43
Now the only other thing you need is DDR3 memory 2GB or 4GB (3.2GB usable by OS).
Also this motherboard can handle up to 32GB DDR3 with 4 slots. So if you want you can get a single 8GB DDR3 stick to future proof for a later OS upgrade.
That should be it.