You have two options. One is destructive and will remove every scrap of data on your system. You will have to reinstall everything. The other way is non-destructive, most of the time. Here are your options.
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<LI>Destructive way. Creative a boot disk. Boot off of boot disk. Type in fdisk at the command prompt. Delete all of your partitions. Create one big one.
<LI>Non-destructive way. Get a program like Partition-Magic or one of the free versions out there. Install this program and you can convert to one partition. In PartitionMagic, it is a matter of moving data, resizing & deleting.
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Hope this helps. Note that you will have to make sure that you make these partitions FAT32 instead of FAT or the largest size possible is about 2GB. Post a message back here if you encounter problems or have questions.