Stirling,
O.K., we're set. Your PC is more than capable of doing what you want. Although, you might consider upgrading your RAM at some point to 128 or better (not a pressing concern, though). Run a stereo line out from your recorder into the line-in on the back of your computer. I'm not sure what sound card you have but I'm sure you have one and it has a stereo line-in. The line-out on your recorder is probably either 1/4" format or phono plug and the line-in on your PC is likely 1/8" stereo single plug so you will probably need an adapter to make this connection (go to Radio Shack). Now you'll have to explore your soundcard's recording functions and figure out how it allows you to record from the line-in, displays levels, etc. Play the tapes on your recorder and simultaneously activate the record feature of your card through on-screen displays. Since your tapes are already mixed-down, you really don't need a high-end sound card to do this. I use Soundblaster Live for this and it works perfectly. If you have the same card I can really give you detailed instructions but you'll have to let me know. Otherwise, your existing card can probably do the job for you but you'll have to learn how to use it. It's good that you have a big hard drive because each minute of CD-quality recording on the PC requires approx. 10MB of storage space! Let me know how you make out.
Mark