I agree with Renac in that when you're using a Tablet PC to surf the web, write notes, draw / diagram, then you're holding it more like you would hold a text book and a 12" display is OK.
Back to your original question though of Tablet PCs with internal optical drives:
Averatec C3500 - 12" display - AMD Athlon - CD-R/DVD
Acer TravelMate C30X - 14" display - Pentium M Dothan - option to get with a DVD burner
Gateway M275 - 14" display- CD-RW/DVDTabletPC2.com
has a good comparison chart.
As to playing games, this is going to be a personal judgment because it has to do with what types of games you're wanting to play, how seriously you're using the machine to do that, and how much of your time on that machine is doing so. If you want to play Chessmaster, Doom, and things like that - sure, people play those on Tablet PCs.
Hardware wise, the second generation Tablet PCs are in-line with traditional notebooks. Most use one of three types of Intel Pentium M processor, which is optimized for long battery life, low heat, smaller space. This is a good choice for Tablet manufacturers because the more you use it, the more you'll want to carry it around with you, and the lighter you'll want it to be.
The Averatec is brand new (August) and there are changes being made to the lines all the time -- for example, changing CPU speed grades. The next major changes will probably be just next year like with standard notebooks, and not until Intel releases its new Sonoma platform with mobile PCI express so can swap out graphics cards.
Since you're using it for school, check out apps like Agilix GoBinder and OneNote to help you take notes, organize, complete assignments, etc. I think the advantages these apps offer will outweigh concerns about playing games.