Well firstly, u'l need a software which has looping support ... something like Atomix studio's 'VirtualDJ' / DSS DJ / PCDJ or any other software which is made for live mixing. There u can use the auto-loops (provided the software detects the BPM correctly)... u need to select the number of beats which u wanna loop here (../1/2/4/8/16/32...)...
The other method is that u can use an audio editing software (something like Sound Forge) n select the exact portion of the song that u wanna loop (i.e. The Start point n the end point), copy it n paste it the number of times u want .. Thus, u'l create a new track ... but if u want a loop to play infinitely, u'l hav to use those live mixing softwares which i've mentioned earlier..