I have a 4400 with YDL and 8.6 on the same partition. However I am running 2.3 and my USB (I have a PCI card for USB) and ADB mouse work fine under YDL. You might try upgrading to 2.3. I also know that USB mouses and devices are know to cause troubles with 4400s. For instance they are not boot able. But I don't know what type of mouse you are using.