Snow leopard won't install on dual booted MBP

When I try to upgrade to 10.6, it says it cannot install because "this disk cannot be used to start up your computer." I've seen others that received this error and fixed it be resizing their OS X partition. When I try to do that in DiskUtility, I get the following error: "MediaKit reports no such partition." I thought it was because I accidentally installed grub to the MBR when installing linux. But I've wiped out the MBR using dd and fdisk. I reinstalled MBR doing fdisk -u /dev/rdisk0, and now the rEFIT partition inspector shows the following:

*** Report for internal hard disk ***

Current GPT partition table:
# Start LBA End LBA Type
1 40 409639 EFI System (FAT)
2 409640 188880887 Mac OS X HFS+
3 188880888 189271513 Linux Swap
4 189271514 195371123 Basic Data

Current MBR partition table:
# A Start LBA End LBA Type
1 1 409639 ee EFI Protective
2 * 409640 188880887 af Mac OS X HFS+
3 188880888 189271513 82 Linux swap / Solaris
4 189271514 195371123 83 Linux

MBR contents:
Boot Code: None

Partition at LBA 40:
Boot Code: None (Non-system disk message)
File System: FAT32
Listed in GPT as partition 1, type EFI System (FAT)

Partition at LBA 409640:
Boot Code: GRUB
File System: HFS Extended (HFS+)
Listed in GPT as partition 2, type Mac OS X HFS+
Listed in MBR as partition 2, type af Mac OS X HFS+, active

Partition at LBA 188880888:
Boot Code: None
File System: Unknown
Listed in GPT as partition 3, type Linux Swap
Listed in MBR as partition 3, type 82 Linux swap / Solaris

Partition at LBA 189271514:
Boot Code: None
File System: ext3
Listed in GPT as partition 4, type Basic Data
Listed in MBR as partition 4, type 83 Linux

If I can't upgrade, will a format and reinstall solve my problems?