Just because it can't be said enough, read the mod_perl guide.
I know Juerd has most likely already done this, but anyone that has not yet done so and is wanting to use mod_perl, stop and read the guide. The whole thing. It is a little ill organized, but then the amount of information and the area in which is related to is sometimes difficult to know. But it IS worth the time. I have solved +95% of my mod_perl issues by looking in the guide.