when your ebe is runnin correctly, and you want to use your own theme you can load FieldRefs from you BlogList to work with.
Open yout blogsite in Sharepoint Designer. In home.aspx you have the Transfrom-XslName statement. Click on it and see the "tagproperties"
Here is a setof viewFieldsXML, where all the fields from your list will get loaded.
<FieldRef Name='Title'/><FieldRef Name='Picture'/><FieldRef Name='ID'/><FieldRef Name='Author'/>
<FieldRef Name='Body'/><FieldRef Name='NumComments'/><FieldRef Name='PublishedDate'/>
all you have to do now, is to type your column-name into it (as you can see my 2nd FieldRef "Picture")
In postlist.xsl you're able to call:
at any place you want. just wrap it with some img src attributes and you're the winner
<xsl:value-of select="substring-before(Picture,',')" />