The B1240 usually comes with a lowprofile heatsink with a fan inside. Even so the only way it'll fit is if you remove the CPU cover and add some higher feet's to the case.
It'll be ok for testing purposes if nothing else untill you get yourself a tower. Another thing to concidere is the fact that the card draws alot of power so the PSU might not handle it.
The shielding can be on or off, doesn't matter (I preferr mine off as I can get to the mb quicker but have a cellphone nearby and you risk it messes with the computer (funny store this, had a friend a while back who ran a BBS, the computer was setup to autostart the BBS on boot. He had the shielding off and had put his cellphone on top of the computer and everytime he found the BBS down while away he would just call home and the computer would most often reboot and wolla, the BBS was back up again in a minute)).
