Did I but wrong equipment?

I am new to FCP - I just bought (4 months ago) an 24" iMac - 2.8 GHz - 4 gig internal memory with 1 TB internal HD with 1 TB external LaCie FW 800. I am running OS X 10.5.2 and just upgraded FCP to 6.0.3. I was finishing a 5 minute 35 second training video yesterday and Sound track pro told me my hard drive was not fast enough to get the audio samples to the program. (I use the external LaCie as the scratch disk) Also - FCP crashed 6 times during rendering when I imported the final mix back from Sound track into FCP. The only way I could render the SD project was to do a short section at a time. Then when I went to compressor - FCP crashed 6 times - so I finally just made a quicktime move from the project with the current settings and compressed it to an upload-able format from quick time. Do I need a better external drive? I have been looking at the CalDigit Firewire VR as an alternative (would be faster for Soundtrack Pro?) and after watching FCP crash a total of 12 times before getting the project out I think I need a better solution than my current configuration if only for my nerves. Any suggestions - could this be a bug in 6.03 (in my short time of usage I never had these problems until I installed 6.03) or inadequate hardware - or both - or user problems (me).

Thanks in advance

Jerry Downs - Denver CO