Building a USB interface.

Hi i want to build a standalone USB Device (using the arduino as the SPI) that can control an RGB light system for a computer (similar to AlienFX but using USB instead of PCI). Now for this i obviously need to learn about USB Protocols USB Interface Compatible Chips that can be used with USB and Arduino SPI

And the main thing i was wondering is, if someone has done this or something similar (just maybe a usb interface). The reason i want to build my own board for this is i don't want to just leave my Arduino in my computer as the actual device, and i also want to build my own little board as well.

Sorry for the possibly newbish question and when i start i will keep you guys/gals posted (link to my blog).

Cheers Rhodderz

EDIT: After looking around some more i found this http://3.bp.blogspot.com/_R7o3lst9P4U/S3ZTB7oD9zI/AAAAAAAAAYY/efnit-tzCIA/s1600-h/18f4550_usb_proto_basic.png Which looks like it will do the job (especially being able to build a program for it using a library posted on the blog) Any ideas are always welcome.

Look at the various designs for standalone arduino using ATMega32U4 - i.e. the Leonardo.

When you say "build my own little board" do you mean design from scratch? Or just assemble one? Such as Leonardino ("Little Leonardo") ATMega32U4 providing USB interface, with uSD socket on the bottom.

Cheers for the response and i might go with the ATMega, i wouldnt mind designing it or just assembling on. This would pretty much be my first actual project like this as before i have just messed around with the arduino and a few shields as im more of a programmer. But i do want to get into building little pcbs to do certain jobs and i know its a big leep but if i have to build one ofr this project i really wouldnt mind. I found this USB RGB Controller schematic online but as a complete newbie im still trying to work out the parts http://electronics-diy.com/electronic_schematic.php?id=1013

Cheers for the Help btw Rhodderz

Well, that ones fine. It uses a PIC18F2550 processor. This forum is all about the Atmel AVR series. A compatible design would be an ATMega328P chip in dip package with a USB/Serial adapter module like this http://www.ebay.com/itm/CP2102-USB-2-0-to-UART-TTL-6PIN-Module-Serial-Converter-/130683943875?pt=LH_DefaultDomain_0&hash=item1e6d5ebbc3 You want one like the BATE make that has the DTR signal available at a hole where you can solder a wire to it.