I've had a lot of problems when using HD Link to convert large .m2t files to .avi, the conversion sometimes freezes with the CPU dropping to about 25% but the hard drive is continually being accessed. I think it might be because the hard drive is close to being full even though there is enough space for the converted file.

Don't let you disks fill above 90% as a rule of thumb.

Finally I've worked out it's dropped packets in the captured .m2t that's causing HD Link to fail. So I've got "stop capture on dropped packets" switched on now in HDV Split.

Drop packet issue are often solved by replacing your Firewire card or adding one if you are using a motherboard based port. Dropped packets means your card is not buffering enough samples and is overflowing before the CPU can empty its buffers.