I've administrated Windows servers from my Ubuntu 10.04 laptop using the default Terminal Connection client. The only problem I see is that you are limited to either standard 4:3 resolutions or full screen, but nothing in between. So on my 16:9 laptop screen, the 4:3 resolution does not work well. Using the version 7 Windows RDP client that is installed with Windows 7, you can many options on resolution but also how you want to send over the details of the remote desktop from sound, usb, added desktop visuals.
The larger problem is from Windows 7 you will need to make sure you enable Remote Desktop, give your account remote access, also if needed allow from Windows Firewall.
For basic needs I think the Linux Terminal Connection client works well enough. Keep in mind that the future version of Windows RDP client will support more features such as sending 3D processed video using the remote computer's video card. These features will not work with non-Microsoft RDP cllients, except for approved third party vendors like Citrix.