It's not a 5th generation video iPod. At minimum, it should be a 30 GB. Anyway, if you're only putting 10 cds on it, even 20 GB is overkill, unless you're planning on doing lossless. But if you go that route, that would put a strain on battery life. My own 30GB iPod holds about 5000 songs and maybe 40 hours of audio podcasts with room to spare.
When you say that it's 3 years old, are you talking about a used iPod, rather than a new but unused one or a refurbished model? The reason that I'm asking is that if it is used, and it has gone through a bunch of charge cycles the battery will probably need to be changed at some point, maybe soon. While the battery isn't user replaceable, if you are somewhat of a mechanically inclined DIY-er, it can be done on the fairly cheap.
How much space you'll need depends on the bitrate you use to rip your cds. The higher the bitrate, the better the sound quality, but with increasing file size. If I'm not mistaken, ripping at 128kbps mp3 should produce a file size that is roughly 1MB per minute. It sounds like you haven't ripped anything to your computer yet. I suggest that you do that. Experiment with different bitrates to find out what sounds good for you.
Depending on your space needs, you can get a brand new player for under $100. And since they have flash memory rather than hard drives, they are smaller and much lighter. Sony has the E436, which is an excellent sounding player that retails for $89 for the 4GB version. I got mine on sale for $10 less at Best Buy. If you don't need any serious bells and whistles (no video or photo viewing) you can get a SanDisk Sansa Clip. Sales abound and you can get a 2GB one for around $30 or a 4GB one for $50, maybe even less.
Should I purchase a 3 year old, 20Gb, 5th gen, iPod or a newer mp3? If I purchase the mp3, I can only spend under $100. Which one is the better deal? Is it better to go with an old iPod or just buy newer generic mp3? With the old iPod, will I be setting myself up for hardware problems because its old? I will basically be using it for listening to music around the house, and in the car. I'd like to put about 10 cd's on it with a few 45 minute speeches. I also don't know how many Gb's I need for that much media? Would the iPod be too much?

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