Sometimes, colors of a picture just melt together and you can't tell what the hell is happening.

Does anybody know some techniques that can be used to help this situation, and/or tracing in general?

I mean, anybody know how to use Gimp or something to make the colors in a photo more distinguished?

You could use GIMP to reduce the number of colours. Go to Image>Mode>Indexed and then set the Maximum Number of Colours to something low, like 20 and you'll have a nice easy image to trace.

Ummm... that sorta makes it worse... In my opinion.

I read a good tutorial on rendering photos with GIMP, but can't find it now

You might try the GIMP Talk website. There are forums, tutorials, and links to TONS of resources, including other GIMP-related websites, forums, tuts, etc. It's a good forum, imo, I've participated there in the past.

[Edit] They're having problems with their site host today, so might have trouble connecting. But keep trying,...

I'm not sure if it's significantly different to judes suggestion of reducing the number of colours, but I know many vexel artists use "posterise" in Photoshop to reveal contours of colour. I'm not sure if GIMP has this effect. Remember that most effects will only produce a guide to work off. If there was a super effective solution you wouldn't even need to hand trace it