I have the n800 OS2007 connected to a nokia 5300 through tmobile $5.99 Tzone. Now I can get on the internet just fine but when I try to use other applications like Rhapsody or Skype I cant connect it always says network error. Am I getting this message because I only have the 5.99 tzone? And if I upgrade to the $19.99 tmobile internet will it work?

The 5.99 plan only gives you access to specific outbound ports. They are listed here: http://wiki.howardforums.com/index.php/T-Mobile_Data
For web browsing, they give you a proxy server running at 216.155.165.50:8080. The other ports are basically for email, and virtually nothing else.
But the 19.99 plan should give you just about everything, although I think they still restrict some streaming services in some cases -- seems to vary by market and how old your account is.
In any case, you can try out the 19.99 plan for a few days, then switch back to the 5.99 plan, and they will pro-rate the charges. Or you can step up to the 19.99 plan if you are going on a trip, then put it back to the cheaper web-only plan when you get back home. They don't make you renew your contract or anything like that for simple changes.

Yup. What he just said. The other advantage with the $20 plan is that you have access to the wi-fi hotspots. I'm trying out the $20 plan now, and YouTube video streaming works, but not incredibly fast. Google Mobile maps is also much faster.