The 701SD variant sports a replaceable SSD (miniPCIe, comes with 8GB) and one DDR2 slot (default 512 MB, upgradeable without further ado to 2 GB). From a software point of view, it looks like a normal 701 apart from the wlan; RTL8187SE which is not supported in the Lenny kernel.
The good news is that there is a backport of the Sid/unstable version 2.6.30 kernel for Lenny that includes this driver. Just install Debian on this system without wireless as per ../../HowTo/Install and then follow ../../HowTo/Upgrade to upgrade the kernel. This supercedes our old instructions for the 2.6.26 kernel. If anyone still wants that to work, probably the best route to take would be to backport the driver that is now in the latest stable kernel for 2.6.26.