Not really I'm afraid. If you're noticing .htaccess files popping up, especially in your root, and you're sure you didn't create them then chances are someone's used a vulnerability in postnuke to 'jack your domains. If it were me I'd be going over all files and the database with a fine tooth comb so see what's changed and when it occured. If possible upload fresh files over the top.
If you find your domains are hijacked then the only advice I can give you is to use different scripts. I have a mate who is beta testing the latest phpnuke Platinum which is purportedly the most secure version of the nukes to date. If you like I could ask him if there's a postnuke > phpnuke converter handy and have him host the files for you to download and install.
Hopefully your accounts weren't compromised though and it's just a bug somewhere!
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