How do I access my U 9.10 desktop from my U 10.10 netbook, and vice-versa?
 

I set a domain name in the U 9.10 PC. It has Samba 4 installed because I needed to connect it to a W7. Do I need Samba to connect to another Ubuntu?

How do I set a domain in U 10.10?

Thanks

What kind of access do you need?
If you only need to access the disk, you can either use samba or look into nfs.
You can get shell access using ssh, and printing is usually setup using CUPS.

You can set a workgroup or domain name in the file "/etc/samba/smb.conf".

I hope this is enough to get you started.

From one linux machine to another you can ssh. You will need to install the ssh metapackage on both machines, this should install both client and server to both machines. Then once this is installed all you need to do is go to Places > Connect to Server. Choose ssh from the drop down menu type in your other machines IP and click the appropriate button. You will be asked to log in and once this is done you can navigate your way around the other Ubuntu machine.

I'd like to share the printer and any desired folder, in fact, I can access those U9.10 shares from W7, where I created the same workgroup that I did in Ubuntu the same way you did (/etc/samba/smb.conf), do I need to install samba in the U 10.10 too to create the workgroup or domain? Is that the only way to add a Ubuntu to a domain/workroup?

To my knowledge Samba is mainly used to connect to windows machines, so I suggest that you follow k3lt01's advice regarding disk access.
This will give you user access to the filesystem, just as you would on the other machine.

Printers are usually set up using CUPS. You open System>Administration>Printing and select Settings in the Server menu. Here you can set whether printers should be published, and if you want to see remotely published printers.

Alternatively you can connect to CUPS in your browser at localhost:631

I hope this gives you something to work with.
Play around and see if you can get it to work.

Good luck