Don't think your investment visa should affect your WH visa so long as you meet the other criteria (under 30yo, aus,nz or irish citizen). You need (from memory):
1. a bank statement showing proof of sufficient funds to support yourself in HK.
2. Return ticket OR proof of funds equal to a return ticket (see above)
2. application form shown here:
http://www.immd.gov.hk/ehtml/evfhk.htm (ID(E)940 & ID(E)940A)
3. Passport photo
4. visa fee
thinks thats it.
Ocean
P.S. if they're taking to long or you don't hear anything after a couple of weeks, send a fax through the embassy/consulate to HK immigration stating that you are leaving whatever country you are in on some date very soon (make it up) and you need your visa asap. Worked for me, visa showed two days later.