Maintaining an Extrenal Drive

I have a 500g Seagate. Last night i attempted to run a back up [i use Ghost] and it said my drive was full. So when i checked 'properties' indeed, it almost was [about 5% available]. So i deleted A LOT of the older back-ups, ranging from 37-41gig each, and still, it said there wasn't enough room... available space was still at 5%.

Again, i checked the properties, and the available volume had not changed. So, now i tried 'disk cleanup'. It emptied the recycle bin, i had no idea the ext. drive had one ... but now it's been working on deleting the 'compressed files' [again, i didnt know they were there] but it's been HOURS and not much change. [the progress bar on the clean up window is only at 1 bar after more than 3 hrs.]

Is this normal?

I've also attempted a 'defrag' but again, windows said there is not enough room to do so. [i'm running XP home]

It does seem some utilities do not work the same on an external drive.

Thanks,

Terese