i would suspect any old card to be up to the job for basic video rendering. back in the days of the riva 128, matrox milennium, rage pro etc 2d speed was benchmarked since it used to differ, but these days even the gf2mx400 can match a x1900xt in 2d rendering speed.
unless the x700 has hardware assistance its gonna be more of an overkill for the system your using it for.
a client who uses a viewmax setup of 16 cameras and a recording system uses a basic ati radeon 9250.
its his video capture card thats doing all the work since its the propriety viewmax card which has 16 video in sockets on the back.
if your going for a single camera then your better off getting a vivo card so you can get video in. any cpu with around 1.5ghz can encode on the fly to mpeg4 with no frame loss. but if you get a card that has AVIVO or something that gives hardware assist then use a high resolution camera that can do 1900x1200 capturing and you will have an ultra clean image of the culprits if its for security use.
remember the higher the resolution of the video to encode on the fly then the faster the cpu requirements will be. thats when hardware assistance will be of great help.
not sure if a x700 has hardware encoding assist but if not then save your cash and go for a radeon 9250 or 9550 since they are passive cooled cards, make no noise, and cheapo to buy. 9550 recommended since it has better features than the 9250 for only a couple of quid more.