Whatzcrackn:
Personally I preffer the old school style of PS2's better than the slim line.  You can easily install a Hard Drive into them which you can play your games off of with out haveing to even open up the PS2.  With a Hard Drive you no longer have to swap disks to switch games.  Plus the games load faster off the hard drive than they do from the DVD drive.
Markvp:
I'd recomend Netmech over in the forums at PS2-scene.org.  He does a great job of installing PS2 chips.