Not sure what you mean by "breaks up in places".
In iMovie4, the maximum clip size is 2 gigabytes. When importing from a camera or converter, iMove will just start a new clip ever 9 1/2 minutes (2 gb), but you don't lose a single frame.
If you're getting irregular breaks, including the loss of video (may be hard to tell, if it's only a frame or two), you either have a cable problem (maybe just not plugged-in securely) or a VHS tape that is a bit out of synch. For that, you might need Time Base Correction, where the hardware will basically ignore the synch data on the tape and replace it with it's own. There are VCRs and video converters that have TBC built-in, but they're more expensive. There are also separate pieces of gear that do only that. I dunno whether digital cameras are available that do this.
First, I'd see if it happens with other tapes, then try another VCR, before spending megabucks on more gear.