Well - I installed Suse 10 alongside WinXP on my home system. I recently upgraded the dying hard disk from 60GB to 180GB (supposedly a 200GB HD - but you know the score).
During the install and after the 1st CD - the system reboots as expected but fails to restart with "grub error 18".
It turned out that creating a boot partition 0f 0.5 GB (probably 100MB would do) fixed the problem. It seems that grub has an issue with large partitions.