i modified the thinclient OS PXES cfg file.NOw i want to create bootable disk of pxes.iso file so that i can mount in Virtual box and check whether it wirks properly.i first created a normal ISO using MAgic ISO.when i try to create a bootable disk using the same ISO it asks for "load boot information file".i dont know which file should i select.
All i want is to create bootable disk of the customized PXES OS and mount in virtual box and test it?

Please take a look a cult-thinclient.sf.net you can download a preconfigured ISO that you can alter with Magic ISO and even you could find a virtual thin client (VMware image) that you can download and run with VMplayer and test your images.
In either case you should specify the ISO as the CDROM or go for network boot and keep the kernel and image on a TFTP server.
Find more at http://codtech.com/wiki or http://cult.codtech.com (under construction).

you can use the isotostick.sh script. it is pretty easy to use. there is also a program called unetbootin. VERY easy to use. i used it because i had to put the .iso for ubuntu on a thumbdrive to put it on my eeepc since there is no cd drive.