I wouldn't use auto-partition when setting up a dual boot. I've never tried it, but I'd be afraid it'd trash my windows partition.
From the sound of it though, you DON"T have enough room. It is telling you that you have 30+10_46 Gb of partitions already, and that's 86. You'll need to re-size one of those partitions (I've heard SuSE and Mandrake have partitioning tools that do this, but not RedHat).. Your other choice is to wipe your hard drive, and start over. It might help to check with grub.org, and search for HOWTO on multi-boot. There is a wealth of good infor out there on this topic.