If you wish to change certain colours for example of integra2 then you just need to edit the css to suit your needs....
If you want a theme that for example has been made for phpBB then there is an incredible amount of work involved depending on the detail of the theme is...
To ask if someone could make a guide would take an incredible amount of time trying to explain all the small details... and then offer continuous support where users do not understand something or find something in the code that is different...
I personally do not see it as being fair just to ask the question can someone make a guide as it is obvious that no one other than someone who makes themes know of the amount of work involved...
Also there is a large number of free themes available for 1.4.0 and even more for 1.4.1 eventually.....
Though you could spend the time looking at how to make them yourself which would save someone a lot of time writing an unlimited guide and full support....