Probably, yes. Especially allocating memory is a OS task and so depends on when the OS would like to get 'round to that. Most OS's are not optimised for realtime performance there. Therefore it's not recommended to allocate memory in programms that need realtime performance.
yes, this makes me think of Matt's words: "is it possible that the low amount of RAM?". Allocating memory from RAM alone isn't such a big thing nowadays (but may be on your old laptop). *But*, if memory is low, this might make the OS swap thing out of the RAM, which is the main problem for real time performance. Swapping stops the program for some time, which may easily exceed the time for playing one buffer. Especially on an old laptop which often has slow disks. I think you (=Matt) should look at this one first...