Thank you everyone for your replies.
I have given the "bulb" setting a go and it certainly allows for longer exposures

.
I am now looking for a way to automatically control the exposure time so that I can take a large number of exposures of a set time. I am using the EOS Utility feature that came with the Canon Camera software but this seems to only allow shots of up to 30 seconds. Is there a simple way to automatically control the shutter open
and shutter closed via a PC for exposure times longer than 30 sec?
I have had a quick look at the Canon TC-80N3 Remote as suggested by Leon, but at $150+...

is there any cheaper options??? The information on this remote seem to do exactly what I am after but I would prefer to use my PC to control the shutter if possible.