Slow RDP from Vista to 2003 R2 SP2 x64

I have a Windows Vista desktop. I RDP into many servers 2000, 2003 x32 and
x64. I have one server 2003 SP2 R2 Enterprise Edition x64 build
3790.srv03_sp2_rtm.070216-1710, when I or anyone RDP's into this server from
a Vista computer the session is very slow. The screen refreshes fine, but a
mouse click takes several seconds to reatct.

I've found that if I run a "netsh interface tcp set global
autotuninglevel=disabled" command on my Vista box the RDP session works fine.
RDP from XP is also fine.

I don't know why this is the only server I'm having problems with. I have
one other 2003 SP2 R2 Enterprise x64 server and its build number is
3790.srv03_sp2_gdr.070321-2337.

Does anyone know what the different build numbers mean. It seems like the
problem server has an old build number??? Is there a way to upgrade to a
newer build?