it all depends on what kind of video editing you wanna do.. all macs in the current line up - including the mac mini - are capable of video editing... iMovie (part of iLife), which is included in every mac is able to handle basic everyday video editing...
you should ask yourself several questions.... what sort of video editing do you intend to do?.... does it involve video rendering, multiple video layer composting etc? what's the resolution & duration of the clips you're expecting to edit? all these questions would help you decide which mac is suitable for you..
i wouldn't recommend you to buy a 2nd hand powermac... No doubt they're powerful machines, but new multimedia editing programs (such as the newly released final cut studio 2 & adobe cs3) are optimized for intel processors... it wouldn't be good to invest so much on hardware that you'd find obsolete in such a short period of time...
there was a useful article that i read before i switched to mac, but i can't seem to find it now... it helped me a lot in terms of choosing which particular model to buy... anyways, it basically categorized users into beginners/normal consumers, prosumers and professionals... beginners are the ones who just use their macs for basic daily use, in which everything in iLife is enough to handle their tasks...The article recommends the mac mini/imacs/macbooks for this group of users...On the other hand, professionals are the ones who use their machines as part of their full time work....Of course, the Pro line is recommended for this group... I found myself to be in the Prosumer group, the group that Apple does not really cater specifically to... Nevertheless, the article recommended that prosumers get the Pro line, as there's nothing wrong with forking out some extra cash for hardware that you'd be able to gradually fully utilize when your skills develop, rather than using an underpowered machine that'll limit your capabilities....
Since you're studying broadcasting (which from your vague description i presume involves a lot of video editing), i guess you're somewhere in the prosumer level.. I personally think it would be best for you to save up to get the Pro Line...But then again, jumping into a Pro model for your first mac wouldn't be a good idea unless you've done lots and lots of research, and you're sure about making the switch... The thing is, your situation is kinda tight.... You WANT a mac, but you NEED to edit videos... You have 2 things you wanna fit to... 1) budget.... 2)video editing tasks... It's usually one way or the other... You fit the hardware to your budget, OR your task...
Going back to your question, a straight forward simple answer would be "
The 2.0Ghz C2D iMac is good enough for basic video editing, but not for broadcast work... 5 minute home-made music videos for youtube/2 hour vacation dvd for personal use/1 hour group-work documentary without complicated effects shouldn't be a problem... go ahead buy the iMac... However, if your work involves a lot of editing with snazzy effects, don't get the iMac"
Personally, i'd recommend the 2.33Ghz C2D Macbook Pro.. Why?
1) It's portable (great for a student who might wanna juggle between working on campus/on-site/back at home)
2) it already comes with a screen, keyboard & trackpad
3) it's powerful enough to run apple pro applications...
4) it's expandable (FW800 external disks are essential if you intend to do a lot of video editing... you should know)
5) you can hook up external displays/lcd projectors easily, in case u need to do presentation work in college etc... you can even hook up the 30" ACD!
6) it's still considerably new, so most probably it'll last you til the end of your studies...
Do your research!!! Check out the system requirements for the software you intend to use.... Find out whether the college you're enrolled in has mac labs or not... Buy something that you need, not something that you want...Think hard before you buy... Let me stress this again - Do your research!!! There's no use buying something within your budget that can't fulfill your requirements, but it's always a good thing to save up for a good investment.... if you get the MBP, i'm sure you'll love it... I know I do