I have an old windows 98 second edition hp computer and I want to install linux over it. What version of linux do I need were can I download it and how do I install it

There are several versions ("distributions") of Linux. The one that I use is Ubuntu (http://www.ubuntu.com/). You'll need to download the .iso and burn it to a CD or order a free CD (https://shipit.ubuntu.com/). There is quite a bit of support by the Ubuntu community, simply Google it or come back here.

Hi,
Since this is an older machine, you may want a older distro. The CPU and the amount of RAM are both considerations. Though many that support the Intel CPU have "386" at the end; most are actually 586 or better which means Pentium or better.
Ubuntu is free and they will send you the CD for free. I have a mchine with Win98SE highly customized on one HD and Centos2 on another HD. Just passed its service life, but freely available from www.centos.org - The Community ENTerprise Operating System (http://www.centos.org/) It is built from only open source on the Fedora core, so it is a great study tool for the Linux+ exam.
Cds can be ordered from Welcome to Linux Cd.org - Best prices for your favorite distro! (http://www.linuxcd.org/) for a price or downloaded from ibiblio linux archive (http://distro.ibiblio.org/pub/linux/distributions/) for the archive at UNC. NCSU and GA Tech have archives near me; but many universities have archives of different sizes. The one Ibiblio seems to have more and give fewer errors.
Peace,
Clarke

Get a list of your system's resources and look around distros like Puppy (http://www.puppylinux.org/) are small

I would recommend Xubuntu over Ubuntu because it contains XFCE, a desktop environment that's highly recommended for slow computers

With a Win 98 type machine we are more than likely looking at a 200-500Mhz processor and 256 or less MB of Ram. Ubuntu is great, however it needs more head room than this system is likely to offer. Dam Small Linux will run on most things or Tiny Core one of the micro distros should do the trick