I had Windows XP working. I then put in a new hard disk and installed Redhat 5 on it. From then i could only boot into Redhat. Further, everyting is very slow. Anothe rproblem is that Redhat does not see my netwrok so I cannot get onto the Internet.
I need to have the choice of booting into XP or Redhat.

Going to need some details here.

• Did you put in a second hard drive, or replace the first drive with a new one? If you replaced the first drive with a new one, did you re-install Windows on it? If there are two hard drives now, you should just be able to go into your BIOS and change the boot device order.
• Do you mean RedHat Enterprise 5? If so, why? And if you're not paying for support for RHEL, you need to start over and load CentOS instead, since a 'free' RHEL will give you NO updates, patches, or bugfixes. Unless you absolutely need RHEL, a more 'consumer friendly' version like Ubuntu, Fedora, or Mint may be better, and might solve your hardware problems right off the bat.
• Does your boot menu have a Windows or Other option on it? What happens when you choose it?
• What kind of hardware do you have?? Saying your network doesn't work, tells us nothing...what kind of NIC, plugged in to what?

very simple
if your hard disck size is 80 gb make 40 gb partation for xp rest 40 gb partation leave it only make one partation for xp install window xp when u complete install xp now you want install red hat linux insert red hat operating cd in to the drive
and reboot the system
u boot from red hat cd/dvd follow the screen option set root password as u want set time zone etc then a menu appear on you screen for partation for partion there show option manual aour automatic or free space for easy you select free space paration aoutmaticaly created in your system if you want manualy for manualy one partation for swap which size is double of your system ram maxmum size of swap partation is 100 mb after swap you creat / partation made it size as you want after / partation you creat 3rd partation as /home size of home partation as u want depend on your hard disk after this process you see option boot lodar here show your window xp partation also hd1 hdi is your xp and next red hat u select first boot red operatiing system next you follow the step install package when all finishe your system reboot now you enter your user name passwor time setting now this is compleate now reboot the system you see table red hat press simple enter you see next option other select other this is your windo xp u can open xin xp or red hat as you chouice enjy