Trying hard to read and understand your question ~ apologies if I've misread ~ repost to clarify please. Your operating system and default file format (FAT32/NTFS) information would also be helpful.
You can backup to your 2nd hard drive (F: ?) instead of disk (CDs?) if there is enough spare space in the total 160Gb you mentioned, including allowing for the temp file space required when you run your games on that drive.
If you format your C: drive, you can only access your 2nd hard drive if; a) you install XP back into the C: drive to access the NTFS F: drive. b) you connect your 2nd hard drive (F: ) to another XP or Windows 2000 PC.
Presumably you are running Windows XP defaulted to FAT32, which is why you can not see the NTFS F: drive?
Of course, that is relying on the 2nd hard drive (F: ) never failing, rather than having your backups on CD-Rs, I presume.
Please post more descriptive information to avoid us having to guess what you are trying to do.