First, to change your name all you need to do is go to the multiplayer tab in the game options (at the splash screen) and you can type in your name there.

You can also change your player name (also called "nick" or "nickname" or "alias") in the game console (typically the ~ key), but this can be a little trickier if your name has a space in it.

Nicknames with spaces work fine if you type them in the console like this:

name "Z o o t !"

As long as you use the quote marks on either side it will work, but if you don't, all you'll get is "Z" for your nickname. When you try to bind or alias a key, though, you cannot nest the quote marks. So while these work:

bind "f4" "name Zoot!"

alias "nick1" "name Zoot!"

These do not, because there is no way to delimit the spaces from the letters:

bind "f4" "name Z o o t !"

alias "nick1" "name Z o o t !"

There is a workaround, though: put the name change inside a config file. Create a text file (using Notepad) named "nick.cfg" in the mod directory. Inside the file, type the following (including the quote marks):

name "Z o o t !"

Then you do your bind or alias like this:

bind "f4" "exec nick.cfg"

alias "nick1" "exec nick.cfg"

You'll need to remember to add the alias to your userconfig.cfg file so it will work the next time you run the game. The bind is remembered immediately and saved in your config.cfg.

You can also do it by using what are called "delimiters". Delimiters are special characters that are interpreted by the console rather than just being displayed. One such delimiter is "%", which denotes a space and can be used in its place.

alias newname "name Z%o%o%t%!"

bind x newname

The letter x can be any key of your choice. If you use "%" with your alias, in your console you will see the name with letters separated with % signs. However when you join the game the server will replace the % with spaces.

You would have to save your alias to the "userconfig.cfg" in the appropriate mod directory, i.e. cstrike for Counter-Strike, or valve for normal Half-Life.