It must be something timing out. Very much a guess, but it sounds like the IDE is looking at / for a resource, maybe network connected, or possibly a clash on IRQs. The motherboard change may be a coincidence.
Other (unlikely) scenarios include:
1) Accessing a DVD / CD (in your path maybe )
2) The IDE always looks for something on a network path. (be honest - did anything else get changed )
3) The usual virus / trojan problems (unlikely as it would affect other apps)
4) There is a delay accessing your temporary file directory
5) Another program is installed that has registered *.cs files
6) Source control program is installed
7) Trying to access a data base (mode="strawgrab")
I presume it is only VC# causing the problem and it happens on a brand new project. Does it happen with VB# (might be worth installing to find out). In fact Visual Web Developer may be better, and then define a new website in C#. See if that has the same problem. It won't solve it but may help you narrow it down. Try disconnecting your networked drives.
If it is a board problem then you can swap back and see if the problem goes away. Obviously do a scan looking for IRQ and address problems. Boot in safe mode with network disabled. It will be slow but you should be able to see if the C# is slower than everything else. Try bios-disabling all onboard stuff (network , soundcard, etc). In the BIOS remove all extra disks, dvd and CD.
If all that doesn't work then it's probably time to go to bed anyway.
Sorry if this looks like a brain dump - it is.
I have a similar problem. I recently bought a Lenovo Thinkpad with Core 2 Duo Processor (1.66) and 1.5 GB of Ram.
I have a fresh installation of VS 2005 and every time I hit the save button it takes about 10-15 secs to save. There is very little else installed. It also seems to load much slower the VS 2003. I am kind of stuck because the University only has copies of 2005.
I recommend using File Monitor and Disk Monitor to find out what actitivy is going on during a save operation. I had a similar problem once and found out that this was related to the antivirus.
I also have the same motherboard and it turned out that there were problems with the nForce4 chipset when used in combination with a Maxtor DiamondMax harddisk. But this normally isn't the issue if you have a Maxtor disk that was manufactured after the 2nd half of 2005.
Thanks for the tip. I found a beta for the VS 2005 service pack. After installing some of the performance issues seem to be fixed (particularly this saving problem).
Just in case that you have the Team Suite or the Express Edition of Visual Studio you can already download the RTM version of the first Service Pack:
The RTM of the first Service Pack for the other Visual Studio editions will be available soon hopefully.