Windows 2003/2007 Upgrade/new computer

Heres my situation.
Currently own 3 computers.
I want to build a new one.
Current three computers have office 2003 standard. Max is three computers.

Problem, I'll have four computers, and if I buy "upgrade" for office 07, one computer wouldn't have had 03 on it.

My question: Can I do the upgrade on three, then uninstall, and re-register 03 (since I've now installed 07, and "move" the old 03 license to the new computer,) and then, "upgrade" the forth computer to 07.

Another thought I just had...does 07 even allow 4 users?
Does Microsoft offer single computer upgrades (ie, 60 bucks for a forth upgrade).

You can buy individual retail packages that will allow installation on a single machine per package. Rather a pricey way to do it. You can also purchase license packages from MS, or through retailers like CDW.
I listed MS's volume licensing page below for a good starting place.
Also, MS doesn't do site licensing. Only on a per machine basis. And you definitely DO NOT want to install it on more machines than you're licensed for, despite what someone before me said. If you did get audited, it'd cost way more than you'd ever save.

It all depends on how many licenses you buy for it. Technically, it should only be installed on the number of computers you've bought a license for.

Ex.- If you bought MS Office Pro 2007 with 3 licenses, you can install it on 3 computers, but there's nothing stoping you from installing it on more computers. The only problem is that if the company is big enough and Microsoft decides to do an audit, you could be fined for having it installed on computers that weren't licensed to have the product on it.

Honestly, if you have a SMALL business and want to install it on more PCs, I wouldn't lose sleep over it.

Hope this helps. Good luck!

I'm not even a small business, just a guy with [too many] computers....lol.
So they don't register online with the software and know that I've registered it on 4 computers instead of three?
I find a company this large would solve this problem quite easily....
Is there really a big chance of me getting audited if I'm sitting at home on 4 computers, not three?
If it lets you install on more than three, how do they know. It seems weird they know you can do it, but can't prevent it. Can anyone explain?