OK, installed Ubuntu, where/how do I find/install software?

[Dan <dan27649@xxxxxxxxx>]

Installed Ubuntu 7.04 last night on a spare PC.

Now I'm looking for software, free / open source.  I went to sourceforge,
but was surprised that they didn't let you select projects that support
Linux, leaving you to wade through all of the Windows-only titles.

Also, if it says it runs on Linux, will it always run on Ubuntu?

And, what do I do with the downloads?  Being a Windows weenie, I'm familiar
with what to do with a "Windows EXE".  But what about JARs?  TGZ's?  GZ's?

Right now, I'm looking at LenMus (http://sourceforge.net/projects/lenmus);
the main page shows:
*Operating System*: All 32-bit MS Windows
(95/98/NT/2000/XP)<http://sourceforge.net/softwaremap/trove_list.php?form_cat=435>,
All BSD Platforms (FreeBSD/NetBSD/OpenBSD/Apple Mac OS
X)<http://sourceforge.net/softwaremap/trove_list.php?form_cat=202>,
All POSIX (Linux/BSD/UNIX-like
OSes)<http://sourceforge.net/softwaremap/trove_list.php?form_cat=200>
but the downloads page has only an installer for Windows!

A nudge in the right direction would be greatly appreciated!

- Dan