Well you run into a few problems useing the Gateway case 1 is all the holes for the screws will most likely not line up Gateway has proprietary boards, Second the case connections for the power switch reset and LEDs will not just direct connect to the new board, and third if you do change motherboards you will have to get a new copy of windows the copy that is on there now will only work with that motherboard.
I recently found this forum, it got me interested in reviving the Gateway. From reading past posts on the 9600 3 rd core , clock interrupt related issues, I am fairly sure my cpu had this problem. Thought I just get a new board and cpu.
Replaced the board with Biostar TA785GE 128M version 6.1 Listed as AM2+ socket and "supports AM3" it fit fine ,uses a few less screws to mount to the case,
Installed Phenom II X4 965 125W AM3 ,
Started up fine with old Vista operating system,
Updated operating system to Windows 7 Home Premium
No problems using all existing wiring and connections to switches and components
I was surprised how easy and smooth it went
Thinking of updating the existing 300Wpower supply for good measure, but all seems fine for now
Plan to put the Bengal board in an older Medion computer with another Phenom I just came across