What you downloaded sounds like a patch to upgrade the source code from one version to the next.
If you want to compile it yourself, then you need the tar.gz not the diff.gz.
But I was suggesting that you download the package from here
ftp://ftp.sunfreeware.com/pub/freeware/sparc/9/rsync-2.6.9-sol9-sparc-local.gz
assuming your on solaris 9.
You will probably need popt, libiconv and libgcc packages well.
Then you can installed it with pkgadd (after gunzip).
But if your comfortable with compiling from source, go for it.
The :: syntax is used when you are running rsync in daemon mode, which probably isnt what you want. If you use a : instead of a :: it will ssh to connect.
I usually use something like
rsync -av user@host:/dir /
That sync directory dir from the remote host to the local machine.
It will append the source path to the target automatically.