nasheeds WITH music falls into one of the three categories - halaal, doubtful, or haraam.
there is EVIDENCE that musical instruments are haraam. majority of the scholars are against nasheeds that contain musical instruments - only very few will actually support this issue. aside from that, if youre still not convinced about musical instruments being used in nasheeds as haraam, then take this issue as doubtful = it is said in the hadeeth:
On the authority of Al-Numan bin Basheer, who said : I heared the messenger of Allah say :
"That which is lawful is plain and that which is unlawful is plain and between the two of them are doubtful matters about which not many people know. Thus he who avoids doubtful matters clears himself in regard to his religion and his honor, but he who falls into doubtful matters falls into that which is unlawful, like the shepherd who pastures around a sanctuary, all but grazing therein. Truly every king has a sanctuary, and truly Allah's sanctuary is His prohibitions. Truly in the body there is a morsel of flesh which, if it be whole, all the body is whole and which, if it be diseased, all of it is diseased. Truly it is the heart."
#narrated by Bukhari and Muslim
or check on www.islam-qa.com
for more info about all this!!