You can start mstsc.exe from the command and use parameters for your custom
settings.
mstsc.exe /w:1440 /h:900
Please see usage page to see more usefull parameters like /span or /public
... (run "mstsc.exe /?")

Signature
Zenon Pilat (MS)
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This posting is provided "AS IS" with no warranties, and confers no rights
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> I'm using the latest Terminal Services for XP connecting to Windows 2003
> Servers. I'm using a 22" widescreen monitor at 1680x1050. TS allows me
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>
> I'm wondering why 1440x900 isn't available?