WordPress, .htaccess and CPU Load: I'm going crazy

I moved my blog here from other host 2 weeks ago, everything worked fine and the blog was doing well. Suddenly it started eating cpu resources and after doing a lot of research i found that it only happens when the blog tryes to use some mod_rewrite via .htaccess.

Now the blog is running with the ugly url default in wordpress: http://www.webmasterlibre.com/?p=660 and everything is fine, if i just turn on the permalinks comes the disaster again.

I can’t loose my permalinks, it’s more than 9 months of incoming links.

Anyone knows why is this happening? My blog doesn’t have too much traffic, i have installed some antispam plugins (akismet and bad behavior) and i’ve checked all the plugins, the theme, the database… I don’t know what else i can do. Please, i need some help