Yes, half height cards almost all come with a full height and half height bracket and as you can see on there, a ribbon cable attachment to enable a 3rd output when used in a full height computer.
I've got several low end AMD cards for basic computers in the past, some have been half height just because they were, they always came with both expansion slot brackets so you can choose which you want to use.
The 5570 is a bit of a pants gaming card, it might be worth shooting off an e-mail to powercolor to ask when their 5770 is available, its got twice the cores, hugely faster memory and bandwidth to go with it, significantly higher clock speed, frankly it will wipe the flow with teh 5570 and probably be, well, 3 times as fast maybe?
http://www.anandtech.com/show/2935/10
Ok thats about the best case scenario when its crazy faster than a 5570, in other games its at least twice as fast. It will probably cost about twice as much but in some situations that will be a lot more than twice the performance, also mentions in the review that due to lack of cores/clock speed its actually lacking a little in media playback qualitys aswell as being much slower for gaming so overall the 5770 would be a brilliant gaming/htpc card.
Maybe ask in the OCUK product suggestion thing or post a thread, one of the guys who do buying at OCUK might be able to find out when they can get some in stock, if not long its well worth waiting.
Obviously you mentioned more older games, but the 5770 is better at everything, not just gaming.