There are tons of converters out there, but I doubt any of them are reliable. ASP and PHP are very different, and to get some things that are in ASP you will need add-ons to PHP, and vice-versa.
If you're converting a large amount of code, the converter will likely mess it up, and you will have to find out what's wrong and learn enough PHP to know how to fix it.
If it's a small amount of code, then it's probably worth learning enough PHP to convert it by hand.
If you still want to try one....
http://asp2php.naken.cc - heard good and bad things about it
http://www.design215.com/toolbox/translator/ - supposedly not as good as ASP2PHP
http://www.google.com/search?q=%22asp+to+php%22 - Google search for others
No guarentees ;)
Hope this Helps,
Snib
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