I hate to just be an echo chamber for Rob and Brian's blogs, but it's important to get the word out to people who may be using the Visual Studio 2005 Team Foundation Server 180-day Evaluation edition that your eval time period may be coming to an end soon if you installed around the time that Team Foundation Server shipped.
Rob has all of the details in his post, including a way to determine when your trial copy may be expiring. Unlike some trial software there's not a countdown timer in your face to remind you, so you just might miss it until you realize your server is down.
And if you haven't checked out Team Foundation Server, here's a link to the 180-day eval copy which you can download. Likewise if you need a client to go with that you can download a 180-day trial copy of Visual Studio 2005 Team Suite. That's six months you can use the trial editions for free, even in a production capacity if you choose to. Just be sure to set some reminders for yourself to buy a full copy in a few months if you decide you want to continue using Team System past your 180-day eval period.