Hey, I've been a lurker for a long time, figured it's time for me to post. The 8100 is pretty new, and there are a few HowTos, but nothing covering everything, so I'll see what I can cover.
First off, you'll need to get your phone connected to your computer... I use Bluetooth, but you can also use a data cable. Here are instructions for Bluetooth
1. Click Menu->Settings and Tools->9. PC Connection
2. Select 3. Bluetooth to use Bluetooth
3. If it asks you if you want to turn bluetooth on, select Yes.
4. Go to Menu -> Settings and Tools -> 0. Bluetooth
5. Select 3. My Visibility
6. Select "Show to All"
7. On your PC, go to "My Bluetooth Places" (you can type that in windows explorer and you will go there)
8. Click "View Devices in Range" in the left hand side
9. Double click on your phone
10. Double Click on "Bluetooth Serial Port".
11. It will tell you what Com Port it is assigning to the phone, this is important, remember it (it's Com8 on my computer)
Your phone is now connected!!!!
Now, download BitPim. Install, then run.
1. Click Edit ->Settings
2. Change Phone Type to LG-VX8000
3. Type in the COM Port from before (for me it's COM

4. Click the FileSystem Tab (That's all that works for BitPim)
5. All of your files are displayed in their wonderful Glory!
Here are the locations for important files:
\Brew\16452\ --- All uploads go somewhere in here.
mf --- My Flix
mp --- My Pix
ms --- My Sounds
lk\mr --- My Ringtones
\dload\ --- This contains information about flix/pix/sounds/ringtones
There will be a files very suggestively named, such as: my_ringtone.dat and my_ringtonesize.dat. These files contain lists of the ringtones, so they need to be updated. The phone will create new files if you delete the old ones, so whenever you add a ringtone, sound, pix or flix, delete the two corresponding files.
Here are some rules: the 8100 ignores .mp3 files, although it DOES know how to play them. In order to use an mp3 file on your phone, you must rename it to .mid or .qcp. You DO NOT have to convert it, just change the extension.
To load a video onto your phone, it must be a .3gp file. To convert files to .3gp, I used Mpegable X4 Live. The company no longer supports the software, but there is shareware available here: Mpegable x4 Live v2.2
Converting is very straight forward, select input file, select output destination, select "Mobile Devices (3gpp compliant)", click the red circle... done.
I highly recommend buying a mini-sd card. I picked up one today from Circuit City with a SD-Adapter. Plug the card into the phone, reboot the phone, and you will have three directories,... My Pix, Flix, and Sounds... put files in there, you won't have to mess with the filesystem ever again. Currently I have two episodes of Family guy converted over, and it's a blast being able to watch those on the phone. Each 22 minute episode is 15.5 Megs, so I can fit a whole season on the 256mb card I have. The video player allows for fast forward and rewind also, I'm working on a way to open up audio files in the video player, so I can put audiobooks on my card and have something to listen to on the subway.