You can have 4 Primary Partitions. To create a new one in Disk Mgmt:
Right click on the C:Acer partition to Shrink Volume. When it tells you how much is available to shrink, choose enough to make your XP partition, then complete shrinking the partition.
Use the XP installer to create a new partition in the space your shrunk, then format NTFS. Xp has a slightly different partition table so you should use the XP installer to format, then install.
Later, If you want to add the 19.9gb free space to your Games partition, use free Partition Wizard bootable CD. Rightclick Games, select Resize and slide the left border over the Free Space, OK. Apply step.