Heh, good luck, that one doesn't look nasty but it is complicated enough. Take your time and do like I said make sure you keep all the screws with each piece and keep them all in separate piles so you can easily work backwards. The video will help.
Looks like you can get the heatsink on eBay too:
http://cgi.ebay.ca/HP-Pavilion-DV900...-/160354335753
Because that's not a heatsink / fan assembly that you'll find anywhere, and if it is the fan causing problems you'll need to replace it (I wouldn't oil it unless I knew exactly what kind of fan it was).
Just be sure it's the fan and not your hard drive, that would be annoying to go to all that trouble and find out it's not the fan.