That's not a feature in Wordpress, though there might be a plugin for it. To get line numbers you need to use an actual code editors like Notepad++.

While I know the WP Editor exists, it's serves as a downright awful 'editor' - so if you are handy, just grab a free FTP and a proper text editor.

If you're on a Mac, use these:
FTP: CyberDuck
Editor: TextWrangler

For PC:
FTP: FileZilla or CyberDuck (PC version)
Editor: Notepad++ as suggested by Christian

Ok you guys are right, i think ill just use dreamweaver. Thanks.

rob

Plus, no undo function after you save in the WP editor window is a killer.

Not that I learned that the hard way or anything....

I find textpad pretty good for this, though for once-offs you could use the code editor through your filemanager in cpanel. :-)

i personally love wp editor for quick fix tho... but i use dreamweaver for major work