where to keep the log file and the mdf/ndf

Hi ,

While going through the book of Kalen Delaney "inside sql server"  I got statement  "A general recommendation is to put log files onto their own physical disk. Here I am bit confuse that we have to keep log file in same hard disk separate derive or in separate hard disk itself. On My DB server has only one hard disk, with three logical partition, so if I keep my log file MDF on different derives will I get the performance.

Thanks in advance for reply........

Regards Vikas Pathak