Rectify Lagness Of 1st Official Skin

Managed to reduce the lagness of my current blog skin, which I have done by modifying a blog template that a helpful guy online help me to create. The limitation of the current blog template is that I cannot put pictures as large as 1024 X 768 on my blog posts which will overlap onto the sidebar. Anyone can fix this for me?

Have not been blogging a while when waiting for the new skin. Won't be blogging much from now on because school term is starting soon. But will always blog on subjects that I find to be interesting.