As Grant mentioned it's better to use Michelle Ufford's scripts or Ola hallengren scripts for the index rebuilds.
I don't think there is any straight forward way to do the parallel index rebuild. It will only rebuild the indexes one after the another.
I think you can try this ...
If Table has 3 indexes I1,I2,I3,
Then Create 3 seperate ALTER INDEX REBUILD commands for each of those indexes and create three jobs and then allow them to run at the same time. I think this will work only for the Non clustered Indexes.
Also online rebuilds are available only in the Enterprise edition.
Please test this method. I didn't test this.
Thank You,
Best Regards,
SQLBuddy.