When you stripe (RAID 0) two drives together, the final size of the combined drive will be twice the size of the smallest drive.
Example: if you stripe a 30 and a 80GB drive together, your final drive size will be 60GB. Get it?
You should always use two identical drives. I.E. Two Maxtor DM+ 60GB drives. Same make/model/size/speed/etc.
You CAN stripe the two drives you describe..but what a waste of valuable space that would be...plus they are different models..prolly wouldn't work too well.
I have two Maxtor DM+ 40GB drives striped at home (64kb stripe size) They are FAST as in 81mb/s burst speed.