yeah, i'd just like to interject and ask you to read up a bit more before you start asking questions.
first, are you talking about a ps2 connection or a ps/2 connection? two different things.
second, there is ultimarc and groovygamegear for the do it yourself panels that connect up to a computer or console. google the names to find the sites.
third, there are many people who offer arcade controls such as buttons and joysticks at awesome prices, like happs, ponyboy, betson-imperial, etc.
fourth, most premade control panels aren't that great, and you'd be better off making your own.
last, just sit back and read through stuff like the product reviews over on retroblast or oscars site. or read through posts here and search for topics that interest you. i wanted to build my own four player control panel when i first got into this, and spent too much for something i never made due to my initial stupidity and inability to think first. so sit back and relax, and study up before you start wasting money, seriously.
p.s. i'm not trying to be mean or dash your hopes, just trying to save you from yourself. i've been there, like we all have. also, go over to project announcements and look at projects first. that'll give you a better idea of what you want.