Congratulations on the pass! Now for the bad news...
If you barely passed the XP exam, you'll need to really reconsider your study methods on the other tests. The client tests are really easy compared to the server ones. I studied only a few days for the Vista one and got over a 1000 on it. The 290, 291, and 299 I studied 2-3 weeks each for and only scored in the 800-900 range.
You can use the OS for years and never touch half the esoteric stuff that shows up on the exams. When they were doing the $25 deal I booked all 8 needed for the MCSE+S, but realized very quickly I wouldn't have enough time to study for all of them before the June 30th cutoff so I just did the MCSA. As for which one to persue at this point it really depends on your target environment. 2k3 is not going anywhere for a very long time, but more people are finally starting to adopt 2k8 and the newer credential could help differentiate you. For some crazy reason I did this just to challenge myself, I got nothing out of it for my current job (but did learn some new tricks I didn't know after 12 years working with MS server products).
What methods are you using to prepare?
I'd highly suggest the official MS books, but they are a bit out of date (especially on the WSUS stuff) so also make sure you check the website on the current requirements and use other resources as well. I had access to practice tests through a online training portal at work which helped a lot. The most important thing though is practice all of the material. I had a setup using 4 VM servers and 2 VM clients (TechNet is almost a necessity for this) and was taking some of the exercises beyond the book. It helped, tremendously.
Thanks for the info darkpaw. And you are 100% correct, I really do need to adjust my study methods. I kind of half assed the XP study. Basically thinking "I have worked with XP for so long, this will be easy".
I am using a prep test question PDF. VTC.com for some videos. So far 3 server VM's and 2 XP client VM's. 1 DC, 1 File Server, and 1 undecided. I may setup it up with RIS, IIS, some other random crap. I have the book from a 5 day class on 2k3, and may end up buying the 70-290 book from Amazon shortly. If I can get off my lazy butt and start rocking some labs, I should be good to go.
If I do well on this exam, I wonder if I can spend a short while studying the 2008 differences and pass that test too. Not sure though. I mean, DHCP is DHCP, AD is AD, blah blah blah.