I'm thinking about buying the lian li PC-50 chassi but because of the sideway mounted psu I'll need a cpu cooler that's not too high.

So I thought about this CoolJag JAC322C


But it says it's made for 1U-servers, does this matter?

1U is referring to the height of the rackmount case. 1U is shorter than 2U which is shorter than 4U, et cetera. A heatsink designed for a 1U case would be low-profile, in which case if it can properly be mounted to your motherboard it may be what you are looking for.

I have a few cases that have a side mounted PSU, and sometimes it is a pain finding a heatsink that will adequately cool the CPU yet still fit properly inside the case. For a while I had a volcano 6 with a slimmer fan (A coolermaster fan that was about a third of the height of the v6 fan) cooling an overclocked thunderbird... my lord was it an inferno in there, average CPU core temp hovered around 75 C.

Does anyone know what's the max processor speed this jac322c can cool?

I can't seem to find anything about it

Did a search and all I could find was that it's a server chip cooler that handles Xeon's.....but no specifics.

P4 has thermal throttling so I guess it doesn't matter about the rating. If you need acooler that small, then you have no choice about performance, as its going to suffer regardless. Just make sure you have a lot of air moving through your case. Here is the manufacturer's web page ...

http://www.cooljag.com/p4_s_JAC322C-A.htm

I'm not too sure if it will fit your mainboard, because its clips do look a little unusual.

My P4 Fan goes crazy nowadays when i turn on my pc, goes into overdrive and then slows down. Its starting to effect my pc now, frequent crashes, total un respoceivness, wat to do wat to do...