That's pretty much the copy+paste answer, but it's in bash syntax, which may or may not work for you.
In general, ANSI codes starting with esc [ and ending with m after some numbers work well, but they're not portable to all terminals. A (slightly) more portable solution would be to use tput
Code:
PS1=$USER"@"$(tput bold)$(hostname -s)$(tput sgr0):'$PWD>'
See the tput manual page for more information.
Perhaps you will find that the codes output by tput are exactly equivalent to the hard-coded escape codes given above. In theory, tput should be portable to terminals which do not speak ANSI, but I don't know of a real-world situation where this would make an enormous difference.
(The code \033 is octal for the escape character.)
