I'm thinking about getting an XBOX 360 arcade pack and I'm not quite sure if I can play original xbox games on this version of the 360 console.
Not without buying a hard drive.
To play original XBOX games you need a hard drive so you can download the backwards compatibility update.. if you buy a hard drive and install it on the Xbox 360 Arcade you will be able to play..
If you haven't bought the Xbox yet I would suggest you wait until July 14.. Microsoft is supposed to announce a $50 price cut on the Premium console bringing it down to $299 just $20 more than the Arcade at $279.. (check link below for details)
Good luck..

yes you can play original xbox games on any 360
References :
http://www.xbox.com
Not without buying a hard drive.
To play original Xbox games you need a hard drive so you can download the backwards compatibility update.. if you buy a hard drive and install it on the Xbox 360 Arcade you will be able to play..
If you haven't bought the Xbox yet I would suggest you wait until July 14.. Microsoft is supposed to announce a $50 price cut on the Premium console bringing it down to $299 just $20 more than the Arcade at $279.. (check link below for details)
Good luck..
References :
http://www.joystiq.com/2008/06/30/report-major-retailer-confirms-xbox-360-price-cut/