Using the information here (showthread.php?t=16340) I did the following;

1) Downloaded 901_net_gfx.lzm and placed it into /BT3/optional/

2) Edited syslinux.cfg, adding:
LABEL eee
MENU LABEL BT3 EEE PC 901
KERNEL /boot/vmlinuz
APPEND vga=785 initrd=/boot/initrd.gz ramdisk_size=6666 root=/dev/ram0 rw load=901_net_gfx
I booted the EEE from the USB disc with the 'EEE' option. Resolution is native 1024x600.

Wifi however doesn't work. Using madwifi I can scan for networks, but wpa_suppliment won't start.
I've also tried ndsiwrapper, but then the card no longer scans for networks.

I don't want to install BT3 to the hard disc, but ofc I'd love wifi to work.

[Update]
After writing a small wpa_supplicant.conf and executing: wpa_supplicant -D madwifi -i ra0 -c wpa_supplicant.conf
I received the error: Unsupported driver 'madwifi'
So I've come to the conclusion that wpa_supplicant was compiled without madwifi support. Not sure how I can fix this without installing BT3 to the hard disc.

As mentioned above, I was following this thread; showthread.php?t=16340&page=2
Specifically this post; showpost.php?p=96774&postcount=11
(Sorry, still can't post links yet...)

I have copied the module onto the disc in the correct place, set it to correct permissions, and added a bootup option into the conf file.

LABEL eee
MENU LABEL BT3 EEE PC 901
KERNEL /boot/vmlinuz
APPEND vga=785 initrd=/boot/initrd.gz ramdisk_size=6666 root=/dev/ram0 rw load=901_net_gfx
/media/disk/BT3/optional$ ls -l
total 47644
-rwx------ 1 tafari root 1724416 2008-10-11 22:16 901_net_gfx.lzm
-rwx------ 1 tafari root 4096 2008-09-08 11:40 cubez.lzm
-rwx------ 1 tafari root 6643712 2008-09-08 11:40 nvidiadriver.lzm
-rwx------ 1 tafari root 40415232 2007-12-13 17:27 pxe.lzm
I do not however have a resolution of 1200x600 when booting from USB, nor do I have working wifi (wpa_supplicant is not madwifi friendly compiled).

This leads me to believe that the module I downloaded doesn't work as advertised, or I have missed a step or failed to install it properly.