DSL is based on Debian, so it is possible to use apt-get after a hard drive install once the dpkg database is restored.
To restore Apt, open the menu and go Apps >> Tools >> Enable Apt
Or, if you are in runlevel 2 (console mode) type "sudo dpkg-restore"
Or, you can grab the dsl-dpkg.dsl from the MyDSL Repository and install it using the directions in 3.1 of this Documentation.
However you get it, once dpkg has been restored, you need to bring it up to date.
To do so, open a root xterm and type "apt-get update".
After the process is finished, you have the ability to grab most anything from Debian Stable!
Now for the warning:
DSL is not derived purely from Debian, if you 'apt-get install' the wrong application you may break something, for instance, the X servers.