Did you have swiftdroid before you installed ICS? if so did you do a titanium backup?

If you did download an apk for titanium from a file sharing website (google is your friend here) (I would download it to the file with adb in) find adb.exe on your PC (you have a custom rom so I expect you have it) then open cmd and cd to your folder with adb in and type "adb install xxx.apk (xxx is the name of the apk)

Then from Titanium backup you can restore the root explorer that was in swiftdroid but it will be a system app because thats how it was backed up.

 

You can instal es file manager free from the market. Then add from there.

 

The problem with this is that market downloads dont work in beta 2 of ICS, it will be fixed in beta 3 so this will work then.

Infact it is fixed now, just waiting for mike to release it, but he found some kernel bugs he needs to fix before we get another release.