A few things.
1. When you say moved to trash do you mean you deleted the folder? Windows does not work that way. You need to go into START -> Control Panel -> Add/Remove Programs and uninstall iTunes and possibly Quicktime as well that should also be listed. Simply dragging the folder leaves other files behind along with reg entries.
2. #1 problem fixer for any problems with devices is going to be to make sure the system is using the most current device drivers. Right click on My Computer (This is Windows XP or 2000 Right?) on the desktop and select MANAGE. (There are alternative ways to get to the manager but we are going to use the tree method that is pretty streight forward.)
In the nested tree find Device Manager. Under that locate Sound/Video/Game Controllers and under that will be their audio card. If you right click on the properties section and select the Driver tab it will give you a rev number for the drivers along with the date the drive was released. Compare that to whatever version is on the sound card manufacturer's website.
If you get me the version numbers and make\model of the audio card I can do the legwork for you and post a link to the drivers.
3. Does the computer meet iTunes minimum specs?
Windows System Requirements
* Windows XP or 2000
* 500 MHz Pentium class processor or better
* QuickTime 6.5.1 (included)
* 128 MB RAM minimum/256 RAM recommended
* Latest Windows service packs recommended
* Supported CD-RW drive to burn CDs, video display card, soundcard
* DSL, cable modem, or LAN-based high-speed Internet connection recommended for buying and streaming music
4. If this is Windows 95/98/98SE/or god help them ME slap them upside the head and go have them buy Windows 2000 or XP because anyone who is on 98 and meets the above system specs should NOT be running Windows 9x. This is not an option. If you have a gun, water BB whatever, force them at gunpoint to get an NT based OS instead. XP home which is still better then 98 IMHO is $99 off of some online sites and while it would be a PITA to upgrade in the long run it is WAY worth it. Be tactful though.
Sorry folks but for some spending a grand or more (Most likely more.) on a computer is not an option so simply telling a person to go buy a Mac isnt going to help but will simply alienate this person keeping them from considering a Mac purchase in the future.
Solve their problem dont complicate things by pissing them off.