This post is in response to several other people who have reported
similar problems:

I installed D4 on a brand new Micron PC with the Intel BX chipset on
an Intel motherboard, and a Viper V330 video card, under Windows 98.

the IDE consistently displayed garbage on the screen - messed up speed
buttons,
trash on forms in design mode - and it crashed when I tried to open
source code files. The trash could be made to go away by turning off the
graphics accelerator, but the system was then too slow, and the IDE still
crashed
after a while.

This problem even appeared on a "clean install" with nothing but D4 and
Win98 on a freshly formatted disk; and it was the only app that messed up.
So I thought it was an Inprise bug.

Eventually I got help from some rather senior people at Inprise.
It turns out the Viper drivers on the Win 98 CDROM are buggy.
The bug is subtle, and it only shows up in apps that use TImageList
components, which D4 IDE uses heavily.

If you have a Viper 330 card, you can get working drivers from either of
two sources:

- The Riva web site; what you want is called "win95agp" and is termed
"Release 2 Reference drivers"

- The DiamondMM site. There are several driver sets there. You can choose
the one that matches your chip set (different ones for PCI and AGP, for
instance).

Now that this problem is solved, I am very happy with D4.