no your panel login is not a shell login.
the directory example.com is created for you. go to 'manage domains' in the panel, check the 'web hosting' column, and see what 'user' is assigned, it should also say 'fully hosted' there. Log in to the user listed there and you should find the directory named example.com.
On shared hosting the question is WHICH IP you are looking for. a-b.dreamhost.com will not be the same IP that your sites are served from. Additionally if you have multiple sites on the same server they may or may not be served from the same IP.
As far as how to lookup ip's, there are many ways. If dns has propagated the simple solution is nslookup. If your trying to find an IP before DNS has propagated then you could click 'DNS' under the domain name on the manage domains page and look at the generated or non-editable entries, the IP your looking for will probably be the first one listed there.
If your trying to find it because you want to view the site before DNS propagation tho, that won't work. Read this: http://wiki.dreamhost.com/DNS_-_Viewing_site_before_DNS_change and this http://wiki.dreamhost.com/DNS_-_Accessing_your_Database_before_DNS_change instead.