Here's what happened:

I go over there, expecting a semi-hard time...

Turns out it's this beautiful Precision 490 (Man, I'd put that box in the middle of my living room!) with freaking Dual Xeon processors and 8Gigs of RAM. Customer didn't even opt for Vista, just XP! All I did was take out the old HD, and hook it up to the new puter... turns out the new one boots from the old hard drive (That wasn't cool - I boot up that freakingly-lookingly-new computer, and what does the customer see: the same thing they wanted to get rid off!)... I turned the Dell cables around, and it boots from the new one (I remember the days when you had to mess with jumpers and/or BIOS settings)!

Then, it was just drag-and-drop...

Thanks to all who have contributed to this succesfull enterprise