you can set up a RAID array with almost any kind of media...mac OS X has a RAID option built into its OS and it's very easy to use. i had an internal RAID set up on my previous powermac G5. i've also set up RAID arrays using external USB zip drives and i once saw someone do it with 3.5" floppy drives - just because he could.
the internal RAID solution you want is only possible if you can get two drives into your laptop...which is probably not going to happen. the other suggestion is to set up an external RAID array using firewire drives...get two (or more) external firewire drives, preferably the same size, and use your RAID software to set it up. i'm not sure what to use on a PC since i'm a mac guy.
now, the question is, why do you want to do this? setting up a RAID array on firewire drives is somewhat useless, as the speed gains from the array are mitigated by the firewire throughput. if you want a mirrored RAID array for backing up purposes, using two external drives is also a poor way to backup, as it is less stable than, say, just backing up to another drive using some backup software.
in sum, it can be done, and fairly easily. but the scenario you present doesn't seem to warrant a RAID array, unless you just want to do it just because you can...in that case, i'm all for it.
edit: this is my 1500th post! w00t!