10 gigs should be fine, as long as you don't plan on storying tons of anything there. If its just to learn and play around with, you'll have plenty of space.
BTW, this would be a good time to learn the Linux partition naming scheme, rather than referring to partitions by letter. Assuming you aren't familar with it:
The basic structure is:
/dev/hdxy
x = a letter, indicating which IDE device the partition lies. It begins at a goes up the alphabet from there, so /dev/hda is the primary master device, /dev/hdb is the primary slave, /dev/hdc primary master, and so on.
y = a number, representing the number of the partition on the device. So, /dev/hda1 is the first partition on the primary master IDE device. Likewise, /dev/hdc3 is the third partition on the secondary master IDE device.
Might seem complicated now, but its easy to get the hang of. The installer might expect you to understand how partitions are named (even if it doesn't, you'll need to know at some point); I hope my explanation was clear