Apple will not upgrade your hard drive for you under any circumstances. Period.
You might be able to get an Apple Authorized Repair Center to do it for you though, without voiding the warranty.
This is true -- when I was feeling the pinch of the 80 gb drive and wanted to upgrade, I found that the local Mac store (not the local Apple store) would upgrade my hard drive for about $90 -- one hour's worth of their labor, plus the cost of the drive. Given that the 160 gb drive I was going to put in there was only slightly more than that, it was going to be pretty painful to pay half the cost in labor. Still not that much, especially considering that the work would be done by a certified technician, so you wouldn't void your warranty, I just couldn't justify it, given that I could probably do it myself if I was just patient and careful.
I've done a lot of building of computers over the years, and taking them apart and fixing them, so I felt fairly confident that I could do the work myself. Taking apart and working on a MBP is *much* easier than a powerbook of any size or any ibook. Had there not been the videos of the disassembly process on OWC for doing this, though, there's no way I would have attempted it. Being able to watch someone actually do all of the steps in (fairly) real time, and talking you through it the whole way, made all the difference in the world in terms of confidence. I just took my time, laid out my workspace for keeping easy track of the different screws, and worked carefully. The only really scary part is the removal of the top casing -- the part with the keyboard in it, and the disconnecting of the keyboard cable from the motherboard. It's sort of a strange connection, more like a tiny snap than anything I've ever plugged in to a motherboard before. I've had the machine in for service under applecare twice since then (for unrelated issues) and they've never even mentioned it.
All told, in the video the guy changes out the hard drive in about 15 minutes or less. I did mine in probably less than 45 minutes from start to finish. Both of these numbers make me a little irked that they were going to charge me for a full hour's worth of labor, as they must have been able to do it considerably faster than that. Had the cost been just $45 (half an hour), I would absolutely have paid them to do it.
All of that being said, if you're not pretty familiar with computer hardware or working on it, I wouldn't recommend it, as you really could mess something up, or even just not get the case back on quite right. Just pay one of the local technicians for it, or else you may even be able to pay OWC to do it as well.