No need for 2 hard drives if you partition correctly... You can setup multiple logical drives on a hard drive, so in all theory you only need 20GB partition for Linux (depending what you wanna do) and then Windows will need about the 30GB, so if you had an 80GB drive split it 30B/50GB etc...
if you need any help with the dual boot then just give me a PM, I will be more than happy to help.