I have Vista and Opensolaris on my laptop. And recently I faced a problem installing Service pack 1 on Vista because of GRUB installed. SP1 did MBR checking and since no Vista MBR present it fails to update Vista. Here is solution:

1. Download MBRFix from Sysint site. It is better to put it on flash drive.
2. Start CMD as Administrator and change working directory to flash with fixmbr.
3. List current partitions:

H:\mbr>MBRFIX.EXE /drive 0 listpartitions

# Boot Size (MB) Type

1 47065 7 NTFS or HPFS

2 Yes 143706 191 Unknown

3 0 0 None

4 0 0 None

4. Save current MBR

H:\mbr>MBRFIX.EXE /drive 0 savembr Indy.bin

5. Fix MBR for Vista

H:\mbr>MBRFIX.EXE /drive 0 fixmbr /vista

6. Make Vista partition active

H:\mbr>MBRFIX.EXE /drive 0 /partition 1 setactivepartition

7. Install Vista Service Pack.
8. Vista completes Service pack installation after several reboots
9. Restore previous MBR

H:\mbr>MBRFIX.EXE /drive 0 restorembr Indy.bin