SOS - VPN from Red Hat Enterprise to Windows XP?

I have been requested to connect to a Windows XP (very current) system via
VPN and am coming from a Red Hat Enterprise Linux system on a cable-modem
behind the usual router/firewall. I'm using the IPSec software that is
supplied with Red Hat. Or, TRYING to!

The parameters given (obviously I won't repeat them here) are:
IP address of host
internal IP address
preshared key (a 16-or-so digit hex string apparently)
user name (presumed Windows-login)
password (ditto)

First, I ran into a glitch with "/etc/network-scripts/ifup-ipsec" which
seemed to clear-up by nopping out an "ip route add" statement as suggested
by a Google search.

The connect attempt said "connect: resource temporarily unavailable," and
the /var/log/messages shows a slew of gripes including:

-> Beginning aggressive mode
-> Couldn't find proper pskey, try to get one by the peer's address
-> HASH mismatched

H-E-E-E-E-E-E-L-P !!

Sundial Services wrote:
> I have been requested to connect to a Windows XP (very current) system via
> VPN and am coming from a Red Hat Enterprise Linux system on a cable-modem
> behind the usual router/firewall. I'm using the IPSec software that is
> supplied with Red Hat. Or, TRYING to!
>
> The parameters given (obviously I won't repeat them here) are:
> IP address of host
> internal IP address
> preshared key (a 16-or-so digit hex string apparently)
> user name (presumed Windows-login)
> password (ditto)

Followup... problem still not solved.

I determined that Windows does not support the "Aggressive" phase-1
negotiation-mode and omitted it. Now generally I am getting messages in
the log such as:

> Ignore information because the message has no hash payload.
> Above message repeated 3 times.

The "incorrect hash" message reported earlier is not happening now. Don't
know why.

I /really/ feel like this should all be a non-issue; that it should be
no-sweat to connect to a Windows VPN server... But I see no HOWTO.