I am currently using webadvert (latest version) is there any good banner script that takes less resources that this one?

I use ShowSell, which can be used with or withoug SSI. It also logs impressions and clicks, has a pretty handy interface, and can be setup to be used on multiple sites. It's at http://www.geocities.com/purelybymagic/script/

Try bannermaster from the people who make Hyperseek - http://www.iwebsys.com/download.html

;)