If you can’t see the polarity of the battery, check it with a voltmeter.
If you're lifting up on the glass, how are you supposed to hold the rest of the phone down? Is it by holding the camera end down with the side of your hand and rotating your hand, or using your other hand (not pictured) on the edges (seems very difficult), or using a spudger in a jack?
These 3 screws actually use 2mm Allen (hex) heads, so try to find one of those first (they come in many metric Allen sets) before resorting to the T8 Torx.
I like to clone the old hard drive contents to the new one (in a FireWire or USB enclosure) with SuperDuper before I tear the computer apart then boot off of it to make sure I won't have any problems.
For those of you having issues with the computer not recognizing the new hard drive as bootable, make sure it's partitioned correctly when you erase it with Disk Utility. GUID Partition Table to start up an Intel-based Mac or Apple Partition Map to start up a PowerPC-based Mac like the iBook G4.