Oh didn't realise that you had 08. I also didn't realise that 08 doesn't have slow motion.
Depending on what you need to do QuckTime 7 might be able to do it.
If you open the file in Quicktime 7 then go to Window - Show A/V controls there is an option to change the speed of playback there and then you could save the file. (It may only be an option in Quicktime Pro, i'm not sure)
I would be hesitant to buy iLife 09 now, it has been out for over a year and could well be due to for an update soon.
I'm sure there are freeware options out there to do slow motion.