Connecting to Ubuntu machine from PowerBook

Question

I can connect wirelessly to my self-build machine running Ubuntu 12.04, both from my Intel iMac (10.6.8) and my G4 PowerBook (10.4.11), by opening Terminal and typing:
ssh -X [email protected]
where 'hostname' is the name of the Ubu machine. The 'ssh -X' at the start is something I latched onto early on in my investigating this sort of thing. I'm very, very new to Terminal.
I only need relatively few commands, I think, to do what I need to do from time to time, and accordingly have learned a few which work OK.
This is the Preferences window for Terminal on my PB :
Regarding the un-selected option "Execute this command (specify complete path):", could I use that to automatically execute the command I noted above so that I could save the tedium of typing what is, unfortunately, a longish username-hostname combination. (I wish I had thought ahead and chosen a really short name for my new machine.)
These are machines in my home, and I'm the only person who will have access to both Terminal and the Ubu machine, so in-home security doesn't even figure in all this.

Answer 1

Thanks for your long reply. I'm sorry to say that I don't really understand most of the technicalities in it. I have an extremely limited exposure to this so far, and have learned a few tricks to achieve what I want.
FWIW, you're playing in the proverbial deep end of the pool here.  The shell can be quite unforgiving of certain sorts of mistakes, too.
Although in my first post I set out the command ssh -X user@user-etc, I can achieve the same effect that I want (or so it seems) by simply typing ssh user@user-etc.
For instance, the command sensors works with or without the -X.
Similarly, I can update and/or upgrade the software by issuing the appropriate commands (via aliases I created), with or without the -X.
With the -X (or -Y), ssh is intending to tunnel X Windows sessions, and (to function) the ssh -X (or -Y) command is issued from an X11.app Xterm environment.  If you're not using remote X displays tunneled via ssh, then you don't need -X (or -Y) here, nor do you need X11.app for that matter.
Basically, I'm happy to acquire the few commands I need to carry out a limited number of tasks.
I'd spend a little time with the bash beginner's intro and related materials including the shell-scripting intro.  If you're going to be using Terminal.app on OS X or managing a Linux box with the command line, you'll need some grounding in bash and related.
What I'm wondering, is whether I can shortcut the whole login process after the prompt, and do away with the need for a password.
That's what I was referring to in that reply, and in the linked ssh no-password article.  (I don't have an article covering connecting to Linux, unfortunately.  There are undoubtedly a few posted around the 'net, however.) 
In general, you can get to a no-password login by setting up the certificate keys appropriately.  ssh can use what is called a public-private key-pair, and the public key can be, well, public.  The private key must be maintained like a password; privately.  You first create a key-pair on OS X as described in the article, or from various other resoures around the 'net.   With the private key kept on your local system (again, as described in the article) and with the public key transferred over onto the Linux system (and into its ssh directories), you will get an automatic login, or you'll be prompted for the passphrase associated with the key-pair.  This passphrase is associated with the key-pair, and is not your login password.
There are other ways to do a no-password login including as setting up Open Directory and Kerberos on your local network, but those are more involved than setting up an ssh key-pair.  Those are going to be more effort to set up.
ARD, screen sharing or CoRD are the other options, and entirely avoid the command-line, assuming the Linux box has RDP server capabilities configured.