Ways to Invest in Chinese Yuan (or by extension, any foreign currency)
1) Go to China, bring your passport, open a bank account. Helps if you speak Chinese. You'll also need a something other than a one entry tourist visa. The advantage of this method is that your account actually will earn (small) interest. Disadvantage is that China is a LONG plane ride away from America
2) Go to Hong Kong. Open an RMB bank account. You can do this in English. You will earn some interest, but less than in China. Also HK has visa-free entry for Americans and is the world's premere free-market environment. Still a long plane ride from home.
3) Open an account at Everbank. Advantage - regular American bank, FDIC insured. Disadvantages - no interest, high fees, high minimums.
4) Buy stock in Chinese companies. Read Jim Roger's "A Bull in China", not for advice on what to buy, but for an overview of all the companies in the Greater China region and the different exchanges and classes of shares.
5) Find another bank in the US that offers ren min bi deposits. I don't know of any offhand, but you might try the local afiliates of a Hong Kong or Chinese bank.
6) Related plays -- those interseted in investing in the greater China market might also look into buying Hong Kong dollars and investing them, as well as buying New Taiwanese dollars and investing there. The entire region is a teeming with economic activity and the region is economically becoming more and more interconnected. Opportunities for astute investors abound.
BAD Ways to "invest"
1) "Forex" trading -- simply the updated version of day trading stocks. Probably 90% of forex traders lose money
2) Paypal, currency exchange outside of major banks, etc.