actually, you do not NEED an intel processor. There are work arounds for that, but having an Intel chip makes things a lot less complicated in the long run. Just wanted to clear that up for anyone running an AMD that might want to give it a try.
As for the OP's question, OS NEEDS to be installed on the primary partition. It cannot be installed,
AFAIK, on a secondary. So to answer your question, you wont be able to keep your vista install easily. You're better off backing up any important files and formatting/starting from scratch.
Now, if your laptop can use 2 hard drives, I
HIGHLY recommend using the second hard drive for OS, and the other for vista. This way you don't need a boot menu... just change your computers boot order in the bios and you're good to go. This is the way I generally run it and works great. It keeps both operating systems 100% independant from each other... just in case. It keeps things from getting messy
If your laptop cannot use a second hard drive, but can boot from a USB device, you may be able to use an external drive but can't say for sure since I've never personally done it.
if you need help, shoot me a PM and I could probably walk you through it. You'll need to find which drivers and stuff you'll need to use though for your machine. You might be better off finding an install guide for your particular computer. Something else that you can do is install it in VMware... you're not yet able to turn on QE since it wont support 3D hardware acceleration, but other than that it works fine. Running full speed for me under vista 64 (vmware 6.5) with 1gb of memory allocated to the VM
good luck and have fun
edit: and one other thing to note, sometimes finding the proper setup for your machine will take a few try's. The first time I attempted it, I ended up re-installing OS about 5-6 times before finding the right configuration. Stick with it, do some reasearch and you'll be fine.