PartitionMagic is a commercial software, of course there is no download. ... find a D version if you really need that.
i suggest borrow another HD and plug into your computer and backup your 6G of data. ( even you've find PQmagic, i still suggest you do this as PQmagic is not always working correctly.) and format yourD:, and install linux. partition it into 3 logical partitions. do not format a disk into fat32 under linux, sometimes it causes your windows slows down.
linux need at least 2 partitons one is for root directory / the other is for swap. (windows use a temporary file for swap) Of course you can choose to have more partitions so that different directory is on different partition. eg, place /home in another partition.
you can differenciate different partition according their size. in windows 98. C: must be the first primary partition. and in your case d: is the logical partion behind C:. I believe it is quite obvious isn't it?