umm the quality looks the same, when you changed it to gif, did you use the already low quality images to convert? cuz if so, thats probably y there was no change.
heres a chart:
good quality - bad quality (this is what you had in the first place)
bad quality - bad quality (this is what you have now)
good quality - good quality (this is what you want)
hope you understand what i'm trying to say.
now heres the question, the original image that you had or the ones that you saved in your PSD (assuming you used photoshop), were they good quality to begin with?
tips for layout: the width is okay, try making the >>tutorials navigation a bit more wide, the text is getting a bit tight there. the content headers, try make it a bit smaller in height, it looks too tall, just a bit shorter now. add some padding in your boxes, the text is touching the edges. try giving the boxes a border or something, cuz it looks like its just floating around.