behringerwell, first off, you probably should save up for the mackies... i used to have the 24x4 behringer, and there were several abnormalities. i forgot most of the problems... but i do remember some channels being louder than others, and some channels developed intermittent signal loss. the mute buttons also didn't mute perfectly... they actually let through a noticeable amount of sound. the behringers also lack the functions of a comparable sized mackie... it's their low quality design and limited function that makes them half the cost of mackies.
now, i bought a 32x8 mackie, and it solved some problems. it's not perfect either though... the mute buttons still aren't perfect, though are probably better than those on the behringer. but it's got a hell lot of routing options.... much much more than the top of the line behringer, i believe. made things so much easier and faster to do.
but anyway, for now, ... as for routing on your behringer... i also used to route my computer through the mixer too. i also have my dvd outs coming in (i have the world's fanciest karaoke system... my gf made me do it!). the mixer's the way to go. but unfortunately... especially on lower quality mixers, there's an inherit addition of noise. check it out: move the fader beyond unity, and you will see, towards the top you'd get an unacceptable amount of noise.
so, the best way to do this is to run as hot of a signal into your mixer as you can. meaning... turn up fader on the mixer all the way, and your amp high too... enough so you can hear the noise floor easily. then adjust the volume on your computer as loud as you can while the noise floor is still acceptable (usually around 1/2 volume). then move the fader to unity and play some loud music. at the loudest parts, the master meter (if you have one) should be just above unity... adjust the trim pot to achieve this.
this procedure should be applied to all your equipment.... that way you will have the least amount of noise possible.
now, depending on the complexity of your studio, you might have other considerations... like outputing the right amount level to effects units... so, you'll have to adjust levels for your own situation. but in general, just make sure all your stuff is calibrated to unity... and try to run balanced lines if your equipment allows for it. read your manual carefully though... even my mackie 32x8 is not completely balanced at all inputs/outs. know which jack is balanced and which is not.
let me know if you have more questions...