should i buy halo 3 or halo odst for my new xbox?

[evan]

i recently bought a xbox 360 and want to play halo online. i know that halo odst comes with all the new maps but do i have all the features of the original halo 3 on multiplayer like the katana and the acheivments because i cant get acheivments from halo 3 campain because odst has a new campain and its a different game... and when im playing odst online am i only playing against people with the odst disk or with people using halo 3 disks?

 

[pazapaza]

if you play, say, social slayer with the odst multiplayer disc, all people with odst disks and regular halo 3 disks will play together. you will be missing some of the origional halo 3 campaign acheivements though. But, the xbox takes the disks as the same game. (if you may or may not have known, odst comes with 2 disks: multiplayer and odst campaign. the xbox will think the muliplayer disk is the origional halo 3, but will not have a campaign.)