At first I was going to reply just like CXIV did without even thinking about it. Which is apparently a mistake, because windows 7 has some pretty high requirements to run. Apparently you need 1 or 2 gigs of ram to run it, depending on if you are using 32 or 64 bit. Compared to Xp which only required 128 megabytes of ram. However, you meet that requirement, so it shouldn't be an issue.

As for it being safe, your not going to cause any damage to anything by putting it in. Worse case scenario is that the computer just wont start. So if you feel comfortable taking them apart, go ahead and give it a try.