From what I know....
MPeg1 or standard associated with VCD is lower end bitrate...
MPeg2 is associated with SVCD and DVD has much higher bitrate and thus larger files and much better looking....
The are both just standards adopted by MPEG...something, somthing, group!!! Mpeg1 obviously first and then mpeg2...
IMO the mpeg1 standrad at 1mbit/sec is often quite crudy above 352 resolutions and only good for lower quality stuff and when filesize is a major consideration. MPeg2 has SVCD standrad of 2mbits/sec to DVD standard of 8mbits/sec