how can i play music from my laptop through my hi fi system?

Try going from the earphone jack on your laptop to the auxiliary in
jack on your hifi.

IMHO is better to use the line-out jack (green)on the laptop with a cable 

jack------------rca (white)
         \------rca (red)

is very cheap but, if you need a definitive solution with optimal
audio quality ....


http://www.soundblaster.com/products/product.asp?category=1&subcategory=207&product=585

First of all, is your laptop a new one with a headphone jacket (I know
it is a silly quesiton, but I ask it anyway).

Second, you can either do it by a wire as it is explained here, or use
a WiFi media player and share your music and media from your laptop's
HD to a unit like LinkSys media player (it is a bit expensive
thought):

http://www.amazon.com/D-Link-DSM-320-Wireless-Player-802-11g/dp/B0001WXTF0

Or if you are in France, you can use  the FreeBox from free.com and
share the music you have on your laptop on the freebox so you can
listen to it or even watch your movies on the TV.

Cheers,
/Farhad

http://www.cnnix.com/remove-feedback-when-playing-music-from-laptop-on-qid-1006051120336/

	set up a better ground of some sort or make sure your speakers are
plugged in all the way

<A HREF='http://www.cnnix.com/remove-feedback-when-playing-music-from-laptop-on-qid-1006051120336/'>Remove
feedback when playing music from laptop on stereo system? </A>

Anything coming from the Headphone jack is going to be only as good as
the Digital to Analog Converter (DAC) on the laptop which normally
isn't very good.  In my opinion (and what I do) is to get something
along the lines of a Soundblaster Extigy sound card that runs USB. 
Then you can take the optical out directly into your reciever.  You
get no noise induced by the DAC or the poor connections on the laptop.

There is always the bought option. This sound bridge allows you to
surf shared directories across your network wirelessly.

http://www.mp3.com/roku-soundbridge-m1000-w-wifi-card/hardware/30/summary.html

There is also the Tico solution. It let's you do the same thing, but
with it's own interface.

For highest quality, try slimdevices.com
But you probably don't need highest quality; then you might try
http://www.overstock.com/cgi-bin/d2.cgi?PAGE=PRODUCT&PROD_ID=1969279&cid=25608&fp=F,
or just run a wire from one of the audio outs on your laptop to one of
the audio ins on your hifi (possibly with an adapter -- it's hard to
say since you provided no info about either your laptop or your hifi).