Here’s a 4 step process:
- Recover any important data from the windows partition by mounting the partition in openSUSE and copying the data to a storage location
- Install windows to the partition it currently occupies: format the old partition with the win CD in the begin stages of the installation and re-use the partition. That will knock out the Linux bootloader – no worries
- Use any of these methods to boot back into openSUSE: Five ways to boot openSUSE when Grub is broken. The first option is pretty straightforward for newbies.
- Reinstate the openSUSE Grub loader using this technique: APPENDIX: Installing a brand new bootloader once you’ve booted into openSUSE
Ask more questions if it gets difficult.