hi frnd there is no need of partition magic tool..!!!!
u can set the partitions at the time of installing linux but u confirm that there is no data in the remaining 40GB
u can make the partitions for linux by choosing "custom layout" at the time of installing .
u can devide the 40GB as
1..root
2..swap
root->37GB
swap->3GB(double of your RAM size);
this is enough
now u can enjoy with linux.........................
see u then bye!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!