There is no "lite" version of Outlook 2003, except Outlook Express. Outlook 2003 is actually the best email client geared toward's tablets - support inking of emails. Inking is not supported in Outlook Express, btw.
What kind of machine are you running it on? I have a M200, 1.5 ghz 768mb RAM tablet and it runs fine. I don't consider it slow at all.