Windows – Open a test TCP connection to a specified IP/Port

I'm looking for a tool that works across windows (xp through 7) that will allow me to open a TCP connection to a specified ip and port. This functionality used to exist in windows xp (netsh diag connect iphost ), but the Netsh diag commands seem to have been removed in vista/7. I've been looking around for something similar, and I've searched Super User, but I can't seem to find anything.

Something that's already built into windows would be ideal, but a small executable that does this (preferably command line, standalone executable).

Edit: I should have specified further. I'm familiar with Telnet and putty, and it is what I currently use, however, I'm in an environment where I have to guide non-technical users through troubleshooting very technical problems over the phone, without any form of remote access (sounds fun, right?). While telnet works, it doesn't explicitly state whether or not the TCP connection was successful; you have to look at the title bar and the contents of the terminal output, which, for some reason, seems to be impossible to users. I'm looking for something with a clear "TCP Connection completed successfully/failed" type response, if such a tool exists.

Edit #2: Thanks to everyone who answered. All suggestions were good, despite the fact that I didn't post as clear a question as I should have. Thanks for the help.