The THF AF1 is actually fairly easy to do solo. I did it at level 41 and could kill the Quads (silver & Garnet) that you need to steal from- but even if you go earlier, and cant kill them- its still very doable.
They are very close to the zone- so you can pull one, head back to the zone, engage it & try to steal. If you miss, disengage, "Flee" the short distance to zone, rest while steal & flee's timers are back up & go try it again. I used this method my first 4 tries- on the 5th, I noticed I could kill the Silver one I was fighting, waited for him to cast a spell (for some reason my steal rate seems better this way), run to the side & steal.
If you see party's in the area, tell them what you are doing just so they know you may be zoning quad's.
You can shoot me a tell if you'd like if you see me on. Here's a great resource- by Famke- a thf who's knowledge has helped me quite a bit.
http://www.bvvp.com/gaming/ffxi/thfaf.html
There was something very rewarding about telling my LS that I just completed AF1- solo^^
good luck