If you buy a custom made computer make very certain that the operation system is legal and you get a re-installation  cd/dvd with it.

Over the years I've had experience with people that bought custom shop made computers and there have been two problems.  First some of them didn't have legal operating systems, the shop put the same system on multiple computers and they had no re-install cd's.  
The second problem that's cropped up is the lack of drivers and support.  Places go out of business and they don't keep records.  You have to dig parts out and hope that there is a part number or something on the video card, motherboard, sound card, etc. so you might be able to go to the manufacture and get the drivers.

Just things to check if you go that route.