You can put the hard drive into another box and it will not erase your disk. Even re-flashing standard ASUS firmware 1.0.7.8 will keep data.
Have a look at this site http://wl500g.info/showthread.php?t=10198.
I have used this in the early days to make sure I could retrieve my data.
You just need to run Linux (i used Ubumtu) on your windows machine via a CD, loading system temporarily.
I have 2 of these wl700ge's - great little units.
Hope this helps