I received an Xbox360 with RROD from a friend.
My brother in law gave me a tip about what X-clamp fix kit to buy and what video to follow, so I ordered it and got to work.
After 2 hours the Xbox was back together with the fix installed and it booted perfectly!
Tried playing a game the day after, the xbox kept freezing and eventually gave RROD again…
After disassembling it again I noticed I used way to much cooler paste, so I removed it and put on a new layer.
And now I have a fully functional Xbox360 that has cost me €17 for the X-clamp fix and about €40 for a hard drive.
Not to shabby I think 
The kit I used: http://www.kamben.bambition.nl/360-rrod-fix-pro-v2-p-1213.html?name=360%20-%20RROD%20Fix%20Pro%20V2 (in Dutch)
and the installation: http://team-xecuter.com/install-rrod/
instruction videos are on youtube and all over the web.
Be carefull not to damage the motherboard!
Now I can start publishing my XNA games to Xbox, sounds cool