What's the difference between Asset Management/Alternative Investments and Private Equity?

Was looking at the Goldman's website and was wondering what's the difference between:

1) PEG - part of the "Alternative Investments' division within Asset Management which 'co-invests' in private equity

2)The actual Merchant Banking/Private Equity division?

Also noticed that other banks e.g. Citigroup have a separate private equity arm and an alternative investments division in their asset management business.

Alternative investments: http://www2.goldmansachs.com/careers/inside_goldm… business_snapshot/investment_management/asset_management/ articles/asset_management_030926121019.html

Private Equity: http://www2.goldmansachs.com/careers/inside_goldm… business_snapshot/merchant_banking/index.html