Citrix presentation server 4.5

Hi, we are running metaframe xp version on window 2000 server for the lastcouple of years and now planning to upgrade to Win2003 and presentation server 4.5.

We have TS licence installed in another window 2003 server domain server but downgraded to 2000.

if the citix presentation server(4.5) is to be installed on win 2003(as our existing appliction server is outdated), do we need to purchase the TS Licence? if so can we install citrix presentation sever 4.5 in windows 2000?

what could be the best solution you recommand for our situation as we are not prepared to spend 10s of thousands for TS licence as all our workstations are runing on WinXP Profissional version.

Thanks