how long will it take to run a full defrag?

Probably a couple of hours.

Difficult to predict the time for a defrag since it depends on variables such as the size of the disk, free space available, level of fragmentation, the defragger's alogrithms, system usage etc.

The windows defragger is very slow and inefficient anyway.

If you want a fast and powerful defragger that defrags everything without a fuss, and does it automatically in the background too, then check out Diskeeper 2009. It's pure set-and-forget and makes life really easy. http://www.diskeeper.com/ has free trial versions

It depends on how badly fragmented it is. Also the built in defragger is much slower than any commercial third party tool like Diskeeper which once set in automatic mode defrags super fast in the background even when other programs run.

For my computer which has windows vista and is only a year old takes about 2 hours.

Looks like yours on the other hand could take atleast double that.

Just let it sit.

it depends the speed of your comuter and the size of your computer

but no matter what it should take more than an hour, and you can still use your applications. you can also clean your hard drive for unnessesary things and it will go faster.

depends on how often you do it. Apparently youve NEVER done it or you would know, so id give it over night.