The N900 was recently granted USB hostmode by MohammedAG and Team (thanks a ton guys), this opens a whole realm of possiblities. First off the requirements:
I bought the following adapter:
Then Install "Enhanced Kernel" v45 from your application manager.
Reboot your phone (should not be connected to PC!!), upon rebooting you will be greeted by a terminal, hit any key and type "run noloboot" quickly. Once booted install H-E-N (note you would need to enable extras devel repo on your app manager). Once installed connect the adapter to you PC cable, and connect any storage device). Click on High Speed USB, the on VBUS on, finally on enumerate, your device light should get on, if it does not the Kernel is to blame.
Once that is done click on "Mount" and the device should show up in you file manager (if it does not as it did with me, go to the terminal, type "root" and "mkdir /media/flash", "mount /dev/sda1 /media/flash", it should show up then)
I also tried a Logitech MK250 Wireless mouse+keyboard, inorder to get this working you will additionally need Blue HID from app manager, once installed reboot phone and connect the wireless reciever, the keyboard would work, and to get the mouse cursor, just fo to app menu and run "mousecursor". It should show up. BE WARNED: Scrolling behavoiur will change in browser after this.
Now run along and hack away!!