So I followed your directions explicitly. My only problem is that if i select to boot ubuntu, refit fades and i see the penquin and then nothing happens. It doesnt boot linux. I have the same setup as you. Macbook Pro 15" 2.5ghz. Vista-64bit Ultimate and Ubuntu 8.04. Windows Vista runs great, and OS X runs the same. Where did i go wrong?
on rEFIt Partitioning tool i see

Current GPT Partition Table
# Start LBA End LBA Type
1 40 409639 EFI System (FAT)
2 409640 465715239 Mac OS X HFS+
3 465977384 524571133 Basic Data
4 524571134 620936368 Basic Data
5 620936369 625142414 Linux Swap

Current MBR partition table:
#A Start LBA End LBA Type
1 1 409639 EE EFI Protective
2 409640 465715239 AF Mac OS X HFS+
3 465977384 524571133 07 NTFS/HPFS
4 524571134 620936368 83 Linux

Status: Tables are synchronized, no need to sync.

Any ideas why linux wont start up?