Most you can do with a 30GB and a 160GB is JBOD (Just a Bunch Of Disks), which doesn't do you any good.
For RAID0 (striping - performance), you need two (or more) disks of the same size, so that is a no-go
For RAID1 (mirroring - safety), you don't technically need same size disks, but the mirror will be as large as the smallest disk; the rest you will not be able to use, so that pretty much takes care of that option too
All other RAID levels require more than 2 disks, so they are no option for you anyway.
HTH
PS: Why would you want to do RAID? I would tend to think that if you don't know what it is and the different options, you probably don't need it.