I understand your concern for not wasting more economies in something that already costs you precious money.
But keep in mind that sometimes "cheap" translates as "expensive" if you consider the chances for things that might not work as planned.
Since this is your first computer ever, you don't want to allow for problems to happen if you can avoid them. And as others have already pointed, RAM memory is not an expensive thing given the hassle that you could be getting yourself for saving on it.
Basically, the more RAM you have the more things you can do at the same time without your computer getting slow or even freezing. For example, you would do some research opening say 30 web page, each one possibly with sounds and or animation graphics, etc. With maxed RAM you might never worry about, while with 1 gb for current systems you could face some glitches. Think of RAM as the size of your car's cabin: the bigger it is, lesser is the chance that you might have to stop the car and grab something out of the trunk before going on.
Image editors, such as Photoshop, are know as RAM-eaters, there's never enough for them.
Video editing depends, and it can be less demanding, for example if you do simple cut/trim editing without applying effects. I've gone that with as little as 250 megbytes. Of course nothing else running in the background.
Converting video, say from DV to mp4, is a third kind of thing: instead of RAM what it benefits from is a faster processor.
Also remember that to capture video from a DV camera (if it's DV you use) there are 2 essential requirementes: your computer must have a Firewire slot to be able to connect a DV camera, and you need a hard-disk that is 7200 rpm, preferably external.
Hope this helps. And yes they are all right, don't buy Apple RAM, look at sores such as NeewEgg. I choose Mushkin, and other ones are Patriot, Corsair, Crucial.
Hope this helps.
