无法安装ADT Cannot complete the install because of a conflicting dependency

安装不成ADT  不怎么怎么办了...
Cannot complete the install because of a conflicting dependency.
  Software being installed: Android DDMS 21.0.1.v201212060256-543035 (com.android.ide.eclipse.ddms.feature.group 21.0.1.v201212060256-543035)
  Software currently installed: Eclipse SDK 3.6.1.M20100909-0800 (org.eclipse.sdk.ide 3.6.1.M20100909-0800)
  Only one of the following can be installed at once: 
    Eclipse UI 3.6.1.M20100826-1330 (org.eclipse.ui 3.6.1.M20100826-1330)
    Eclipse UI 3.6.2.M20110203-1100 (org.eclipse.ui 3.6.2.M20110203-1100)
    Eclipse UI 3.6.0.I20100603-1100 (org.eclipse.ui 3.6.0.I20100603-1100)
  Cannot satisfy dependency:
    From: Android DDMS 21.0.1.v201212060256-543035 (com.android.ide.eclipse.ddms.feature.group 21.0.1.v201212060256-543035)
    To: org.eclipse.ui 3.6.2
  Cannot satisfy dependency:
    From: Eclipse Platform 3.6.1.r361_v20100909-9gF78GrkFqw7GrsZnvz0JWNTeb6fue6896L (org.eclipse.platform.feature.group 3.6.1.r361_v20100909-9gF78GrkFqw7GrsZnvz0JWNTeb6fue6896L)
    To: org.eclipse.rcp.feature.group [3.6.1.r361_v20100827-9OArFLdFjY-ThSQXmKvKz0_T]
  Cannot satisfy dependency:
    From: Eclipse RCP 3.6.1.r361_v20100827-9OArFLdFjY-ThSQXmKvKz0_T (org.eclipse.rcp.feature.group 3.6.1.r361_v20100827-9OArFLdFjY-ThSQXmKvKz0_T)
    To: org.eclipse.ui [3.6.1.M20100826-1330]
  Cannot satisfy dependency:
    From: Eclipse Project SDK 3.6.1.r361_v20100714-0800-7Q7m6DDaKf5o2z-L9LxPSe6ygafz-KKIqk1rr_3j4dn7J (org.eclipse.sdk.feature.group 3.6.1.r361_v20100714-0800-7Q7m6DDaKf5o2z-L9LxPSe6ygafz-KKIqk1rr_3j4dn7J)
    To: org.eclipse.platform.feature.group [3.6.1.r361_v20100909-9gF78GrkFqw7GrsZnvz0JWNTeb6fue6896L]
  Cannot satisfy dependency:
    From: Eclipse SDK 3.6.1.M20100909-0800 (org.eclipse.sdk.ide 3.6.1.M20100909-0800)
    To: org.eclipse.sdk.feature.group [3.6.1.r361_v20100714-0800-7Q7m6DDaKf5o2z-L9LxPSe6ygafz-KKIqk1rr_3j4dn7J]