haha, sure thing.
D3 One Click is a tool you can use to root the phone with your computer. As you might have guessed, you plug the phone in, click once, and it takes care of the rest. Download and how to instructions can be found here:
[Root X] D3 1-click Root Method - Works on GB.602 and GB.605
A ROM is basically a modified version of android you can install on your phone. I'll let you do your own research on which ROM you'd prefer, but I recommend CM7, Shuji, ApeX or MIUI. To install a ROM:
1. Root your phone
2. Install ROM Manager from the Market
3. Flash Clockwork Recovery in the ROM Manager app
4. Download the ROM you want to flash to your SD card. Know the location it's in (which subfolder on the SD)
5. Open ROM Manager, click reboot recovery
6. Select "wipe cache" and then "wipe data/factory reset" from the main ClockworkMod Recovery menu (using the volume buttons to navigate the menu and camera button to select)
7. Select advanced>wipe dalvik cache
8. Go back to the main menu using the back button, select install .zip from sdcard
9. Navigate to the ROM you downloaded, select it with camera button, sit back and wait
10. When it finishes, reboot. Congratulations, you have flashed your custom ROM!
You need to make sure that the ROM you flash is compatible with your system version. Any ROM based on the Froyo (.340) kernel will brick your phone and you will need to SBF. Be sure to read up on the ROM you want to install to make sure it will work properly. In doing things like this regularly, you WILL brick your phone at some point and have to SBF. It's impossible not to screw stuff up once in a while so don't be afraid to make mistakes and learn as you go, and it always helps to make backups frequently which can also be done through ROM Manager