Although Microsoft has a list of qualifying system specs there are a ton of individual devices that are being found that do not work with windows 7.

Your best (And most sound) bet is to grab one machine from each model you are looking to upgrade and do an install of windows 7. You can evaluate each example to determine how well windows 7 would fit into your enviornment from there much better than you could with a SQL query (Which would only look for system specs).

It is worth mentioning that any upgrade to Windows 7 at this time is questionable. Personally, I would wait at least until SP1 before attempting to start upgrades. By that time, MS should have taken care of the first batch of bugs.

We will be looking at app compatibility also, the planning and surrounding processes will be thorough and lengthy. In the first instance we want to report on hardware compliance. It may well be that we dont upgrade until SP1, or depending on how many workstations need hardware upgrading we might not upgrade at all. 

in NSv6 that is uses for determining application upgrade requirements. I believe the title is for XP, but that is cosmetic. The parameters you can specify include memory, processor and harddisk size\free. See if that doesn't meet your requirements.