Software

Remote PC Access 2.2
Remote Administrator 2.1

http://www.download.com/

Windows XP Pro has a built in remote desktop that's ideal for what you're trying to do.

PC Anywhere is certainly the tool of choice for remote support needs but it is costly. You can buy bulk licences for "Host only" to distribute to your clients.

It might be worth checking out Microsoft Live Meeting (formerly known as Placeware) for application sharing. They have free monthly trials. MSN Messenger also has built in application sharing.
Creating a script that will do system audits that users can email you or post to a website would also be an alternative. The company I work for currently has a web based system scan as well as brower settings scan that posts results straight into the call logging system.

I assmume you're wanting to take complete control of a remote machine though? Personally, I believe being a good remote support person means being able to step the end user through anything you need to do with just a telephone. They become your eyes,ears, and input control. Obviously some cases are harder than others and I understand that nothing beats "seeing it for yourself" even if only remotely.

I'm a huge advocate of educating users at every chance you get. Coming from an extremely under resourced support team with the bulk of users in remote rural locations our motto was to try and eventually "do ourselves out of a job!" by teaching users how to fix their own problems.

Execeptional telephone skills, superb product knowledge and a passion for educating your users is always going to be your cheapest option and makes for a more satisfying customer experience.

Enjoy!