Mobo/CPU recommendations for skinny space

[Fear The Weasel]

Hi there, I want to build a computer into a rackmouted case and I'm trying to chose a motherboard and cpu. Case will either be 83.1mm (preferable) or 127mm (acceptable) high. (to clarify - no components can stick out further than this from the mobo)

Basically I was thinking something along the lines of an AMD Sempron (I don't top of the line preformance) but I'd like to get some peoples opinions about what would be the best way to go. The thing is the case is quite skinny so I'd be stuggling to fit in a cpu with a giant heatsink and fan on top of it. I looked at Mini-ITX boards but I can easily make do with a Micro-ITX mobo and get much better specs for my cash.

Please any advice welcome. (I'm not a complete PC noob, I've just been using laptops for the last 5 years so I'm a bit outa date on desktop hardware. )

[smb]

I am going to assume your refering to a 1U rack case. you can run any type of cpu in a 1U case, but you definitely have to have an excellent low profile heatsink. I think thermaltake makes an excellent solid copper solution.