No GRUB after install openSUSE 12.1

I’ve recently installed openSUSE 12.1 from NET installer. At the end of installation there was an information that GRUB cannot be installed because of some partitioning troubles.

I have Windows 7 with these partitions:
sda1 - windows boot partition (100 MB)
sda2 - windows filesystem partition
sda3 - ntfs partition
sda4 - ext4 with openSUSE

Can I replace somehow this windows boot partition and install GRUB or something? I’m not in common with boot systems. (I don’t want to repartition my HDD or reinstall linux).

You should read up on some of the basics
http://forums.opensuse.org/content/26-install-opensuse-win7-guide.html
Re-Install Grub Quickly with Parted Magic - Blogs - openSUSE Forums