Ususally, when I record from my synth, I use the line in port and just record live. I've been trying to do this via the midi port recently and although It works, I'm getting a load of lag between pressing the keys and sounding the note.
   I was wondering if anybody knows a way to get around this?

you mean, the midiport lags?  (if that's what i understood)  --oh yeah, duh, that's what the post title is :P  i'm retarded!

it's probably because of the fact that it's doing some processing of each note (ie: piece of data it's recieving) so that it can determine the sound it should create...  as far as a way around it...  that's a little rough.  i know how hard it is to play without hearing what you're doing, and it's even harded when everything is offset :P

as obnoxious as it sounds, the only thing that i can really think of is to record using the line in port, mix a copy of it down and put it on some sort of music player.  put some head phones into the cd player or whatever, switch the synth to the midi port, set the computer to then record.  i'd turn the speakers from the computer off and then push play on the cd player or whatever it is and play along with the cd-player recording.

the notes would still be delayed on the pc recording, but at least the timing would be right, and then you could do a shift on the recording so that it lines up right?

that's kind of the "sledge-hammer to the wall" way of doing it i suppose, but unless there's another way...

it's either that or you do the line-in port for the actual recording, and then just write out the notes in a midi program for the sake of having a written score of the arrangement :P

just don't send me hate mail, unless it will truely make you feel better. 

what kind of hardware do you have? if you've got a card with zero latency direct monitoring this shouldn't be a problem. If you've got a synthesizer with a midi port and a line out, buy a mixer to use as your monitor mixer and then plug the output of the computer to the mixer AND the sythesizer line out to the mixer... and plug the MID out of the syth to the input of your computer... if you've still followed me this far... disable the "monitor" setting in your host app (Cubase, Nuendo, Sonar, Pro Tools, whatever you use turn of the "monitor" button) and then adjust the mixer volumes so you can hear your solo as it should be. That way you don't have latency when listening to the sound. If you've got actual latency on recording, i.e.  the sound PLAYS back, lagged, then you've got more serious issues with crappy hardware. Anyway, that should work i think.

btw, latency is caused by the sound travelling through the Hz based frequency governed computer busses such as the PCI bus, the on die cache, the north bridge, south bridge and CPU itself, all have timing restrictions, i.e. they only return signal every certain number of cycles. So if your sound goes in, it's got a guaranteed delay before it comes back out. If you've got a card with direct monitoring, it essentially splits the signal and routes one signal into the computer and one signal directly back out the main jacks before even hitting the PCI bus, thusly no Hz based cycle wait queues, thus no latency. tada.