I am nowhere near as knowledgeable or experienced as other posters here but if this is true:
I would make sure those files are backed up multiple times and that those backups are readable. Everything else can be repaired or replaced. I would probably wipe the existing Windows install and reinstall. That fixes the immediate problem. Now either dual boot or run a VM. You can run parallel systems and have time to become familiar with replacement apps, port spreadsheets & databases etc.I also installed SUSE Linux on an old PC, but partitioning the disk was a nightmare, and I'd prefer not to have to go through that again. However I do have a business to run that lives and dies on the old MS Office files. I'm perfectly willing to build new DBs and spreadsheets in Open Office, but I need to be able to open and read the old ones.
I would also consider, after reinstalling Windows and apps and everything is working, create an image of that install. Clonezilla gets good reviews. I just installed Windows 7. It took close to 4 hours with drivers, updates apps, etc. etc. etc. Restoring an image takes about 30 minutes from DVDs.