so you dont have a specific app you want to test, you just want test the physical server itself.
Lets see. Since you may be putting it in a live enviornment, what will you be using it for? i would start by testing it with what ever it will be or could be used for. if its a possibilty, use em all. I would also try running a large number of transactions at the same time. These could be set up using jobs, stored procedrues and cursors. They should be doing simple and complicated selects, updates, inserts and deletes. You should also try doing some admin tasks on databases. You can do some on ones currently being used, and some not as ones you will eventually perform. If you have existing datbase you can put on them as a baseline, do that then create your transactional testing processes. It will take a bit of work to come up with all the processes to test it.
But after ive said all that. If you are unsure of a machines hardware relibility (not performance ability) but its relibility, i would not put it into production if you could help it. If you do have to, then you should put things on it that you do not care as much if it has problems and could lose all data from the last backup. You should then make sure its as backed up as possible and freeqly so that data is not lost. IF you are putting Enterprise addition on it, i would use log shipping. IF not, i would use frequent backups to a different server.
I hope this helps some.