Not sure on model numbers but certain late P4 NetVista towers (the ones with the backwards-leaning cases with flat fronts, whose front panels extend further than the top of the case) take what appear to be standard ATX mobos. PSU is a problem, it's fairly weird-shaped, but they actually have decent PSUs to begin with so if you're not building a monster you might be able to get away with it. 200-something watt output but they're decently reliable for OEM stuff.
Now I'm not sure, might be ThinkCentre towers.
This is the case style, anyway:
Show Image
(http://www.laptopenterprise.com/images//sku2019.jpg)
Thinking back on it, the PSU length is the problem. Standard units fit but interfere with the optical drive(s). Shorter drives may fix this, not sure. Don't quote me on this! It's been a while since I was in one of them.
Here's what the PSU looks like in that thinkcentre:
(http://geekhack.org/attachment.php?attachmentid=10034&stc=1&d=1273979877)
NetVistas were also made in those "fender" towers. My particular intellistation happens to be leaned with the back fenders. IBM used that whole design in general for a lot of their later tower models.
The PSU should be standard, the ThinkCentre S51s on the other hand used PSUs that are probably impossible to replace!
(http://geekhack.org/attachment.php?attachmentid=10035&stc=1&d=1273980056)
(http://mod-system.net/auction/images/2009830n1420m34.jpg)
If you're able to tell, the PSU isn't a square, there is a part where it has a "balcony" over the motherboard. So you'd either have to get one half that size, or also balcony over.