Splitting NZB files into smaller files?

How do i split an nzb file into many smaller files.
For example, i want to download a file that is 300mb big, but the client i use only lets me download files that are 200mb each. I have tried opening up the nzb file in notepad and splitting it in two, keeping the heading and footing. I then downloaded the two files and added the suffix .001, .002 etc. for use with hjsplit. It seemed to work, but when i played it, the video had interference and stopped playing.

Can anybody help me? and please dont tell me to get a better client.

Cheers,
Rich