if the drive is constatly clicking, it could be old and on its way out, or it could be "thrashing"
the drive might be fragmented.

its very hard to explain, but after you delete stuff on the hdd, the computer sees it as free space and plonks new data there (excuse the technical term ) after a few months you can imagine the data is all over the place, the computer knows where it is though, but as its in so many differnt places it just takes longer to get (imagine your tools neatly laid out on a bench at the start of the day, and then by the end they're usually round the car, inside it, on the scuttle etc etc)

you could try a drive fragment.

go to my computer
rightclick on C:\
properties
defragment now
analyse.

this will give you an idea, i.e if it looks like a barcode of red and white you need to defragment. then you can choose whether to defrag it or not. do this at night before you go to bed though as it can take up to a few hours to complete, and the comp doesn't really like anyother activity going on whilst the defrag is taking place.

sorry if i sound patronising, its not meant that way but some people know more about computers than others. and my little instructions are based on xp, cos its what i've got.