A good place to start looking is the MS site. They have a bunch of info on them and can direct you to testing centers. For a help desk gig I don't think you would need an MCSE (Microsoft Certified System Engineer). But I think they phased out the MCP (Microsoft Certified Professional).
As far as preparing for the test(s) (Depending on what track you take the MCSE is usually 7 or so, the MCP was 1 laughable 1 I think) goes there are TONS of options. Its like an industry unto itself. Everything from expensive classes at places like New Horizons (I think they charged 7k-10k for the whole MCSE track) to just buying some books or software for self study. Whats best for you would depend on where you are starting from knowledge wise and how well you can learn on your own.
But like I said, for help desk stuff I wouldn't think they would want an MCSE, though I could be wrong. If they don't have the MCP anymore they do have the MCSA (Microsoft Certified System Admin I think) which you only need to take 3 or 4 tests for.
Pretty much no matter how you decide to prepare expect to pay $125 or so (thats what they were when I did them) for each test.
Plenty of info on the MS site and the links there. Best of luck.