Instructions for getting software from a PC to a Mac can be found at

http://home.earthlink.net/~gamba2/pc2mac.html

Although 7.6.1 is indeed a fine OS, it isn't free, and doesn't really offer much for that model beyond 7.5.5. Apple offers the latter as a free download (install 7.5.3 first, then upgrade):

http://download.info.apple.com/Apple_Support_Area/Apple_Software_Updates/English-North_American/Macintosh/System/Older_System/System_7.5_Version_7.5.3/

Finally, problems aren't always fixed by using the latest OS. Indeed, sometimes it's the "upgrade" that causes them. If the manufacturer of those peripherals has recommended a certain OS version, I'd start there. Apple offers several versions of System 6 and 7 for free (just fish around the parent directories of the link above).