You can get CMS Static Block urls in following ways:
1) To get Base url in CMS block,
Syntax: {{store url=””}}
2) To get Skin url in CMS block,
Syntax: {{skin url=’images/imageName.jpg’}}
3) To get Media url in CMS block,
Syntax: {{media url=’/imageName.jpg’}}
4) To get Store url in CMS block,
Syntax: {{store url=’mycmspage.html’}}