Thanks all for your replies.

I try to answer all:

My full setup:
Asus M4A785TD-V EVO
2x 1TB SATA HDDs
1x SATA DVD-drive
AMD Phenom II x6 1090T CPU + Noctua NH-D14 cooler
8GB RAM
1x HD 5850 GPU (monitor, projector and TV is hooked in this card. Also (TV)audio goes through this card via HDMI cable)
no extra fans (120mm and 140mm is included in this case)
AXP 750W PSU
3 USB devices is connected all the time
Antec 300 case ( http://www.antec.com/demo/ThreeHundred/ )

No overclock at all. Everything is in stock/default "settings".

GPU runs kind of hot, 70-75c and fan speed is  ~64-70%.

I use GUIMiner with these flags: -v -w 128 -f 40 (i don't have dedicated mining machine) and i mine in Deepbit. Here is what my statistic page says: Last 24h: 0.24 BTC
This card produces ~280MHash/s

I think there is all so far

EDIT: OS is W7 64bit and 11.6 driver
EDIT2: I pay electric myself, not living with my parents