Citrix License

If someone could tell me that if i need to purchase the license for the Terminal Service of the Citrix or the MicroSoft or both which i don’t think so. Here is my problem…
We have Citrix 1.8 running on windows NT 4.0 and now we try to upgrade hardware and citrix to MetaFrame XP on windows 2000. I have installed for testing environment and i am running into the licensing problem. I am putting the quote together for my boss, but i don’t know which license that i need to purchase. If someone can let me know i greatly apprcicate it. I know that the Citrix needs TS in order to run. I am searching all over internet but i could not find the answer nor call up the Citrix. Much Thanks!
DP