Well ½Mex , you're going to get a shed load of suggestions but I'll start with a question and then a suggestion.
Assuming that the laptop Win98 is not Second Edition and assuming that it is not networked -?- I would take out the Hard Disk.
Go down to PC world or Maplin and buy the IDE connection adapter to enable you to plug the Laptop's HDD into an IDE cable in the shiny new desktop. Like the disk in front here.
When the PC next boots up it'll find the HDD as a new drive and you can then do the transfer.
About £10. Have a good trip.