Download and run Memtest86 to check that your RAM is still good.

http://www.memtest86.com/

There are a few things you need to know to upgrade your RAM.

1. What RAM do you have now?

Brand, Speed and Timings/Latency are all important.  It is best to match as closely as possible to keep your system stable.

You can open your case check the RAM itself or download a utility like Everest http://www.majorgeeks.com/download4181.html  to check.

2. What RAM does your motherboard support?

If you have the motherboard manual, it will have all the details you need here.  Does it have 2, 3, or 4 sockets for RAM?  What combinations are supported?

If you don't have a copy of the manual, you can probably find it online.  If you don't know the model, Everest can tell you.

While DDR2 RAM is getting really cheap, DDR is still expensive, so you will be better off if you can add to your existing RAM instead of replacing it all.

im water cooling my E6420 and have it from 2.13 or 2.14 or watever stock is to 3.2ghz. and thats nuthing. its runnin at bout 14-16c idle. prolly hits round 24c at peak. and u can barely hear it.

gtarmanrob

Where is your radiator?  14C = 57F.  You can't cool your CPU to below ambiant temperature without phase change cooling.

If that is all your budget permits, I would wait a bit...  depending on what you use your PC for.

For most games, your graphics card would be your bottleneck.  Cutting your RAM to 1GB from 2 would limit multi-tasking performance - which is the one thing going to a dual-core CPU would improve.  You would probably see better performance for audio/video encoding types of applications, but not much improvement in anything else, so I would say wait and save your money for a better uprgade later.

I think I might need a soundcard.mejia13fernando

You can see if you like the onboard sound first... then get a sound card if it is not good enough.

Like maybe downgrade to E6400 CPU or E6300mejia13fernando

Don't get E6400 or E6300!  The E6420 and E6320 are the same price and have double the L2 cache!

True. Is it possible to go cheaper?mejia13fernando

You could go with this RAM for $95: http://www.newegg.com/Product/Product.aspx?Item=N82E16820231087

You could also cut the PSU to $70 (after mail in rebates) with one of these PSUs... Both will provide very stable power and support SLI if you want to go that way in the future... 

http://www.newegg.com/Product/Product.aspx?Item=N82E16817371002

http://www.newegg.com/Product/Product.aspx?Item=N82E16817103512

I would personally get the Antec True Power Trio TP3-550.  It has 3 12V rails, 5 year warranty and is very efficient.

That would save about $100 without hurting performance.

Definitely NCIX.  They also price match competitors and for all canadians outside of BC, there is no PST.  That saves me 8% on everything - which is ususally more than shipping.  They also have great weekly sales on tons of stuff and occasionally have free shipping deals (like this week).  I just put together a gaming system with E6420, 2GB Corsair RAM, GeForce 8800GTS, 20" widescreen LCD, HD, DVD, Vista, etc. for only $1430 CDN including shipping and taxes: http://www.gamespot.com/pages/forums/show_msgs.php?topic_id=25665626

I also like Direct Canada (also in BC with free ground shipping on orders over $300), Anitec (Alberta) as well as Canada Computers and PC Village for local pickup near Toronto (or to price match with NCIX).

Tiger Direct is too expensive when you factor in taxes on pre-rebate price and shipping.