How to Find, Remove Malware?

Hi,

I found my wordpress blog infected with malware a few months ago, so after backing up the database, I removed the entire hosting account and had it reset to default, then reinstalled wp 2.3.2, am using only the default wp theme and the original database. Now I find I have two files called starboom.cn and loadbalanse.cn loading when my blog loads (not the original malware I had which no longer shows up), and zonealarm tells me my site is dangerous. How to do I remove these again, and if I have to do a complete reload again, how do I prevent further infections?

Thanks, Matt