Scalability from Postgresql

hi all,

i plan to develop a internet database an for this i need a database;-)
i dontt now which, i think about adabas or Oracle but they are very expensive
for me.

now my question:

How good can i scale PostgreSQL?

Such as following scenario:

i start with 1 CPU and with 1 HDD an 128 MB Ram
next step i give a 2 HDD and try to Symlink or copy the data dir
next step i give more ram 256 and i think about RAID*
.
.
.
and so on.

What does the db do?

Primary i have ~50000 Datasets and primary 6 Tables and many many relations
tables, i think there are many joins or subselects!?!?!

i hope you understand what i mean ;-)
if i on the wrong way to think please also help me.

thanx

al ;-)

PS: Please forgive for my bad english ;-)