There's a fake blood tutorial here: www.guerrilla-productions.org/Tut...html

Completely depends on you budget, how effective you want the F/X to be, ability of your F/X person(s).

Blood is very simple, and cheap. Karo syrup and food colouring is all you need. Play with the colouring yourself and do some screen tests to see how it will look with your DPs lighting. Make several batches with different consistencies. If you want some texture to it, brain matter etc., mix in a little oatmeal. Brewing some strong, dark coffee and mixing it in gives a great dark, arterial look (in my opinion).

Heads popping off is very different, depending on the mood and tone of your film. If you're looking for realism, you're looking at plaster casting, as well as negative and positive molding. Liquid latex, and foam latex is very expensive, and requires lots of practice. If you're doing a campy sort of film, maybe realism isn't exactly important; try manaquin heads, or foam wig heads. Maybe re-writing your script with some other gore gag is a better option.

Organs and entrails are also easy and cheap. Find a local butcher, pay him a visit, and get some animal guts. They're the real thing, just make sure you refridgerate them. Also make sure you wash them, as you're not going to be eating them, you can use cleaners and solvents to make sure no nasties are present (do this often).

You didn't mention it, but if you're looking to do wounds, check out this site:

www.polytek.com/store/merchant.mvc

It's reasonably priced, easy to use, and looks great.