I really was asked how to do this- so I thought I'd post my dummies guide/step-by step instructions in case they are of use to other Galaxy neophytes.
Step 1: Download the Xenopus mRNA FASTA file to your computer
first I make a new folder on your desktop- I called mine " FASTA files"
go to this url: http://www.xenbase.org/other/static/ftpDatafiles.jsp
click the + next to sequences to expose the list
choose you file type- lets assume you want the X.laevis mRNA in FASTA format
click the blue FASTA link, then save to your computer ( in that new folder) with the .fasta suffix ( I had to rename it XenopusmRNA.fasta as it reverted to unnamed)
Step 2: Ipload the file you downloaded to Galaxay.
open a window at Galaxay ( usegalaxy.org)
on the left is a tools menu column- click the 'get data' link to unfold the menu here
click the 'upload file from your computer' link.
click 'choose local file' button
locate your file/choose it
under 'Type' drop down menu, scroll down to fasta
don't choose anything under genome ( xenopus not there yet)
hit start button at bottom of the window
A green bar will fill to 100%, and your file is now over on right hand side of the screen, under history
hit close button at bottom of the window
Your FASTA file is uploaded, and you can use the FASTA manipulation tools and other stuff in Galaxy that are back in the left column...it will automatically read your Xenopus file now