How do I remove sun 5.10 os from a hard drive?
Is Sun 5.10 the only thing on the drive, no other data/partitions/booting operating systems?
If yes then install your favorite Linux distro and select using the entire hard drive. Be careful which hard drive you select.
If no then we will need to look at the partitions and what ou need to keep.
If the Windows 7 drive is alreay in use on the system the next part of your question is easy. Set the Linux hard drive as the primary boot drive, install your distro to the other hard drive and it should recognize the Windows hard drive and add an entry to the boot manager, easy.
Can I access both drives on a system?
Linux will be able to see both Linux file systems (likely ext3) and NTFS filesystem for Windows. Windows will not have access to the ext3 Linux file system.
As far as distributions go, I normally recommend starting out with either Ubuntu or Mint, both are very easy. Ubuntu can be booted from a CD/DVD in order to get used to using Linux.