Is it a problem to put a "regular" fan on top of your case?

Ummm my top fan in my Antec 1200 is exhaust...........so if yours is as well you are impeding airflow not helping it. If your computer is running hot enough to require that much extra cooling then take the side off and use a big fan to blow on everything that way. What exactly do you have running that hot?

Nothing at all -- like I said, I'm new to building, so I think I'm just being overly paranoid. Using Speedfan I've yet to see anything over 50C, even after playing some graphic intensive games. So it's probably completely unnecessary?

(BTW I don't think this case has a "top" fan -- it has a side and a rear fan.

That case must have an optional top fan. Your temps look fine to me but you would be better off adding case fans where case fans are supposed to be mounted. Looks to me like that case included 2 x 120mm fans. 1 in the back as exhaust and 1 on the side as intake?

That case can handle 5 x 120mm fans. 1 x 120mm intake in the front 2 x 120mm top as exhaust then the 2 included. All you need to do is buy 3 more 120mm fans. That will give you the best results.........much better than what you are doing in the picture  

I like Antec TriCools myself as they are 3 speed and almost silent on low while still moving quite a bit of air. They are available in just about any color LED or without LEDs at all if thats what you want. Others will argure about fans and I am sure there are better ones out there than TriCools but I have used them in quite a few builds ( I usually use Antec cases and they come in them stock ) and been very happy with both noise and air flow.

Remember front and side blow in the rest blow out. You want negative pressure for the best cooling........basically more air being exhausted than being blown in.

BTW remember these fans are optional and your temps look fine to me. This is just a "how to" if you decide to add them.

Yup,
^ bump that, if you want lower temps,
go with the 2 fans in roof option first,
Moto

thanks so much, this is very helpful

one thing I don't understand, though: how do the optional fans work?

my motherboard has "CPU_Fan" "SYS_Fan1" "SYS_Fan2" and "PWR_FAN"

I've used three of those already for the 2 stock fans and the cpu fan.

But my case is supposed to be expandable for at least two more. So how would those work? Where do they plug in?

Ususally you wont fin more than 2 case fan jacks on your mobo. It's possible to buy a 4-pin Molex-to-fan-jack. Alternatively, you could buy a Molex fan adapter that has multiple fan jacks.

Splitter/adapter:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Adapter: http://www.newegg.com/Product/Product.aspx?Item=N82E168...

thank you!

am i right in thinking that all fans have to be connected to the motherboard somehow? or are there "always on" fans that only have to connect to the PSU?

yes, you have 'always on 100%' fans that plug into the molex's on the psu line,usually sidepanel/roof/front fans are like this
you only have the cpu/rear exhaust casefan on the mobo so that the system can monitor whats happening to them, not essential, but nice to see  
Moto

I have an Antec 1200 with 7 x 120mm and 1 x 200mm top case fans. I also have a 120mm fan on my CPU cooler. The fan on the CPU cooler is the only fan in my case attached to the motherboard. All the others are just connected to the power supply. The fans themselves have 3 speed switches on them......no need for the motherboard to control them. And yes they are always on. They just connect to a standard molex connector and you can daisy chain several together if necessary.

When using this adapter do the fans shut off when the computer is shut down or are they always on as long as power is supplied to the psu?

No they turn off with the computer. There is no need to cool anything when the computer is off.