The < symbol looks fine under Tahoma for me (Win7/64 as well). Are you sure that's the font you're using?
Other fonts have special behaviour when it comes to displaying some characters, other characters might be font-linked. It's generally an issue with the font itself, not mIRC.
I did not have this problem when using older versions of mIRC (<= 6.35) - and I'm sure I'm using Tahoma. I also tried using '<' in version 7.07, same problem.
EDIT: It seems like the script I'm using, nbs-irc, is not that compatible with mIRC 7
