No way, Strict is what you want.
If you were learning how to do a sport, would you want a coach who just encourages you all the time and never tells you what you're doing wrong, or do you want the coach who will tell you YER DOIN IT WRONG every time you screw up until you do it right?
Well, I want the second coach, even if he seems like an @ss, because I will get better from it.
Strict doctype lets the validator tell you ALL your mistakes. Transitional just hides them to make you feel better about your code.
If the page looks awful with the addition of a doctype, it means the page was specifically coded to look Most Jawsome in IE5 back in those heady days of Geocities, grunge bands, and the pre-dot-bomb bubble. Like, when animated gifs and flaming letters and a little "Best Viewed In Internet Explorer" badges were the rage.
Maybe you want to totally ditch the template and get a modern template. Those exist. It might me a LOT easier to deal with.
example of a site which has not-bad css-based templates for free: http://www.freewebsitetemplates.com/
except of course I would recommend changing their Transitional sissy doctypes to a manly Strict : )