Powerquest PartitionMagic can help you, I remeber PM7.0 will be able to do it. You can try that one, but please remeber one point that all your data must be backuped before you want to merge two partitions.
PM7.0 is directly working in Windows environment. Namely, you can merge two partitions in windows environment. Whatever,risk will always exist for any cases, backup your data should be first step.