I would like to move my budget from MS Excel to Org-Mode. I currently have
one Excel sheet per month with all the transactions as well as a summary
sheet that uses sumif functions.

Assuming the following format for the monthly table:

#+tblname: january
| date | transaction | amount | category  |
|------+-------------+--------+-----------|
|   01 | iga         |     50 | groceries |
|   01 | echo        |     30 | car       |
|   02 | iga         |     47 | groceries |

How can I get the following summary table?

| category  | january | february |
|-----------+---------+----------|
| groceries |      97 |          |
| car       |      30 |          |

I found this post on the mailing list that suggest to use babel:
http://www.mail-archive.com/emacs-orgmode@gnu.org/msg22736.html

However, I need help to understand how I can put the resulting sums inside
the summary table.

Thanks,
Carl