Darwin (the underlying OS in OSX) is based on BSD4.4, so generally speaking, it is Unix.
lorcet222, log in to a command prompt (as root), and execute the following command:
pico /etc/passwd
If you don't have pico, you'll have to use another (harder to use) editor. Anyways, though, look for a line that begins with your username. You'll see something like this:
samba:x:1005:100
wner of samba files:/home/samba:/bin/false
Now look in the sixth colon-delimited field (in this case it says /home/samba, yours will be different). That is your home directory - where you will be when you first log in. Now if you change that to another directory, THATS where you'll start. Just be sure that you have the rights to be in that directory.
Let us know how it goes.