blocks

morning
i was hoping you could help me
i have created a website with your theme - thank you very much
i have a left bar and in the middle and right i have the blocks set up as two across and five rows down - so i can fit in 10 articles per page
sometimes if i have an article (a long one) the article overlaps the article below it
is there any way i can prevent this happening...?
look forward to your reply
regards
shyam