|The SYSTEM UNKNOWN means it's not formatted.|
Two things can cause that. The first is that it was partitioned but not formatted between the time it was last used and now. The second is that since it was partitioned in another PC, it's not being seen the same in the computer it's in now. I've notice that problem most often with drives moved to and from old compaqs, which is your situation.
If it was partitioned then you're pretty much screwed. If it's because of the PC switch then if at all possible put it back in its original PC and copy the stuff off from there. Or check the original PCs cmos settings for that drive--the cylinders, heads and sectors--and set it up that way in the new one.
Also, it looks like it was partitioned as FAT16 which has a 2 gig maximum.