Hmmm… It’s been so long since I did the wa/ga thing with TextFugu; looking back on it, it’s actually not that good an explanation now that I think about it. The best way to learn the difference between the two is to just go out there and see it for yourself. Obviously that’s a little much for a beginner, but just referring to は as the topic marker/particle and が as the subject marker/particle is probably sufficient in the mean time – it gives you the basic idea of the differences, but you wont get a grasp for the ideas behind it until you see it in lots of different situations. As long as you *get* that “topic” refers to “the topic of conversation” while “subject” refers to “the subject of a clause”, you should be ok.
Also, when it comes to *reading* は and が, read は as “as for X,…” and が as “X is” – I think that helps more than anything. It kind of fits in with the Japanese style of speaking: often where the sentence begins with は, they’ll kind of hold the あ sound and trail off (as if they’re saying “Uhhhhh….”), before coming back in the with the main part of the sentence (e.g. 「これ はぁぁ・・・ なんですか。」. As for が (or should I say「「が」はぁぁ・・・」), it’s just kinda said as part of the sentence (e.g. 「すし が 好きです。」).