Checkout UltraMon, allows that plus a lot more when running more than one
monitor.
Specifically, it allows the taskbar to span across the entire display or it
allows two separate taskbars with optional both show everything or each
shows just what's on "it's" monitor.
It also adds a fair number of screen management routines, e.g. swapping
windows to display, maximize to entire desktop, saving/restoring icon
positions etc.
It has one particularily nice feature if you're a gamer that plays OpenGl
games. As OpenGl games don't usually run when multi-monitor i enabled,
UltraMon has an option that when you start that game it'll disable the extra
monitors with the option to re-anable either when finished the game or "x"
minutes later (apparently some OpenGl games only object to more than one
display when starting, after that it's ok?).
There's even a "mirroring" feature for those of us who run two separate
video cards rather than some dual-head (which usually includes this in
driver). Optional which monitor is doing the mirroring.
Seems stable, XP Pro, 512 ram, Radeon 64 DDR VIVO and Xpert98.