I dont know for sure... but downloading shit from PSN and playing online uses a fair amount of bandwidth. To my knowledge most DSL services give you a pretty limited amount of bandwidth per day/month. If you exceed the limit they'll slow your speed to a crawl or cut your service completely.
Again, I dunno for sure cause I always used cable and wifi for my PS3, but a DSL connection might be too laggy for online gaming anyway.
I'm sure you could get online with the dsl... I just dunno how practical it'd be.