seo question with old url structure

hi all,

the site I currently run used to be live a few years ago before it was taken offline for 3 years. when it was running a few years back, it ran a different forum software than it runs today, and nothing was carried over from the old site other than the domain name.

when I was looking in my google webmaster tools dashboard the other day, I noticed that it had a lot of crawl errors from the old site url structure. should I redirect users to my main page if they try to hit a url from the old site? if so, what's the best approach? use .htaccess?

here's part of the old site url structure:

http://mysite.com/viewtopic.php?f=1&t=1

thanks!