There's nothing to be nervous about. No PROPER script or application should use sudo gainroot directly in scripts or whatever, so IDEALLY, nothing should break beyond your ability to do things as root.

If you have sudser installed and it works as advertized, you should be able to do the same things as rootsh does, just with different commands. Honestly though, I'd just uninstall sudser, then install rootsh. And if you really want, you can always install sudser back on afterwords. You DID manage to somehow install both - unless you installed sudser after uninstalling rootsh.

If you remove sudser, update your catalogues / "check for updates", and then still can't install rootsh, you can download it from the Maemo package interface (maemo.org/packages), put it onto your N900's USB storage or microSD card, and then click on it in the file manager, which will install it with HAM.