I've been running Vista for a good month or 2 now and today was the first day that I needed to use Telnet.  It's not something I would use everyday, but on occasion I do need to use it.  Well, when I attempted to run it from the command line I got a command not recgonized error.  Assuming that Microsoft had pulled it from Vista, I ended up using Remote Desktop to connect to another machine I have here and then used Telent to connect to the hardware in question and got things running again.  Now with a little more time I went searching and found out that it's not gone - it's just not part of the default install.  So if you want it back, here's what you need to do. 

Start / Control Panel / Programs, then under the Programs and Features section, click on Turn Windows Features On or Off.   You will then be prompted with a list of features (like the ones shown in the attached image), just scroll down and select Telnet Client and away you go.