Looking for advice for work PC build.

The company I work for is updating our data storage software next month, and we'll need to get three new computers. I'm looking for recommendations to pass off on them for either three "cheap" store bought towers, or a parts list so i can build them for him (boss).

Basically, all that's needed would be the towers (three to be exact). They will be connected to our current network, and will only be used for internet access, and running our data software, as well as basic storage like internet file downloads, etc. (500G should be plenty per tower). Won't need high-end graphics, as these computers wont be used to gaming, so either decent integrated graphics, or a low end card is fine.

I think the only issue that I've been told is that the new software runs on Windows 7 32-bit.

The current work PC specs are:
Windows XP
Pentium(R) 4 2.8 GHz
508 MB Memory

(Like I said...these are literally just basic office computers, but they all suck, and we're wanting something newer, and a little more up-to-date). I'm not posting a budget because i don't have one although he said Best Buy was trying to sell him on some $1200 towers, to which I told him to tell them hell no. These are simply build suggestions I'm passing off to the company. Any help is appreciated.