I second the ASUS comment, and have nothing but success with the 4 boards I've owned by Asus.
http://usa.asus.com/products4.aspx?l...60&modelmenu=1
I'm not sure what kind of prices you'll see on that board, or availability in Poland for that matter, but it's a good mid-range board that has every feature that you'll probably ever need.
That motherboard coupled with the X2 3800 should be nice and quiet since it uses heatpipe technology instead of loud fans.
For memory, as has been stated before, shoot for 2GB (2 1GB sticks in dual channel) If that's out of your price range, than go for a single 1GB stick and add a second matched stick when funds permit.
Finally, cases are mostly an asthetic choice, although airflow does come into play. Be very cautious of the power supplies that come with cases as they tend to be very cheap and extremely over-rated. A cheap 500W power supply often times is the equivalent of a 300W quality unit. The power supply is one of the most important pieces in the entire PC, so make sure you get a quality unit from a good manufacturer.