Cornelia -
I think the issue there is that the newer, larger drive (the "Slave Drive") is actually the newer Serial ATA (SATA) format. These drives have totally different connectors - two small, thin "blades" rather than sets of pins. There are indeed adaptors to connect the two formats, but they're not usually over-complicated - the one pain can be the old "molex" power connector, but you have to deal with that if you're putting an older ATA drive in anyway. Connecting an older ATA drive is, indeed, quite simple (but I won't press the point, and I certainly wouldn't call you an idiot to be cautious about trying it).
Regardless, your main system drive is (nominally) 60GB, of which you have 24GB free, and the large "Slave" drive is (nominally) 250GB, of which you have 210GB free. This is a good chunk of space on the secondary drive, so unless you're dealing with high-definition video, it should stand you in good stead for a while. If you're leery about adding more internal drives, you could invest in an external drive - again, Seagate and Western Digital have good models, and you can go to an online retailer such as Newegg and check out reviews. This drive would connect to the back of your Mac via the Firewire 400 connector. Your Mac does not have USB 2, so I would not recommend a USB-only drive.
So, to reiterate, provided that you save your iLife projects to the second drive, you should be good for now.
I'm not sure what's going on with that optical drive - it may require re-mounting (ie, taken out and put back into the drive bay, or even just have the mounting screws checked), and if that doesn't work, you can get a new drive relatively cheaply (around $30 for a new Pioneer drive with faster CD/DVD read/write and dual-layer capability).
Matt