I'm assuming you meant 333 memory and the gigabyte is the 7vrxp or the 7vrx which only support 266 Mhz front side bus but 333 mhz ram. Let me know if it is a latter 333 MB that supports the 333 fsb and ram, the answers will change (see comment at bottom). Options:
Forget a RAM upgrade and the MB is good too. The Duron is choking the life out of your system!
1). Not much point in buying a Barton since your MB probably doesn;t suppor the 333mhz fsb (see recommendations). There is some benefit to using a Barton but you will have to fiddle with the MB multiplier and fsb to get the full rating on the 7vrx family MBs. Also, it is a very good overclocker!
2). I'm not a big fan of the Throughbred class of chips that are available from 1800-2600. The higher speed chips are heat pigs with too little surface area. But they do have a niche.
3). There is a new 266 mHz fsb chip coming out called Thorton. It is a Barton with the onboard cache reduced to 256meg, FSB slowed to 266 mhz (and purely my speculation - I think the multiplier will be locked so it can't be overclocked to compete with Barton).
Right now I'm sitting on a proc/MB upgrade waiting to see if AMD gets it's head out of its butt (and have been for 15 months). But, if your dying to upgrade (and with a 1.3 Duron I would be) options are:
First choice go with the retail xp1800 throroughbred chip $66 at essencompu.com (free shipping and retail comes with a new stock heatsink).
Second choice if you can live with the duron a month longer see how the pricing and the benchmarks on the Thornton shape up (I expect a retail XP2500 thornton at ~$75 based on AMDs pricing structure).
Third look around for a used Palomino xp1900, with a heat sink, from someone you can trust. (price should be ~$50).
Fourth if you are tech savy or have someone who can help. Buy the retail xp2500 Barton and set it up to run xp2500 rating with a fsb 266 for now. Then you have some interesting overclocking options. (<$100 with shipping and stock heatsink included at essencompu.com).
Any of the above will double your system speed and add 50% or more to your gaming frames per second! Remember the Duron heatsink is useless, it must be replaced with something good to cool the faster chips!!!!!!! Figure $20 bucks for a heatsink if you buy an OEM processor (no heatsink included).
If you really have a gigabyte board that is truly 333 mhs FSB go for the retail xp2500.