Given everything you've listed, your best bet is probably
http://www.zwcad.org/. It covers all those requirements and then some, though the main drawback is the download size. I can't recall the exact file size since it’s been a while since I used it, but I doubt it’s small enough to pull down on an old-school dial-up connection.
Regarding other CAD software, I highly doubt there's anything else that fits all those criteria while remaining lightweight enough for a quick download.
That said, as a student, you can pretty much grab almost any version of AutoCAD from
http://students.autodesk.com/ provided your university is in their database, which I assume it is. Just keep in mind this is a student edition intended strictly for learning purposes, so printing is disabled and includes a watermark.