This is completely off-topic so don't be surprise if your question is reaped, but (if i even understand your question correctly) perhaps you can try using HAVING instead of WHERE?

select `from`, group_concat(text) as con 
from `database` 
group by `from`
having match text against ('windows xp')
order by con desc
[download]

I must admit however that I really don't understand how match text against ('windows xp') works. :/

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)