Is a vpn to an external network a security risk for my network?

I have someone who wants to establish a secure vpn to another oirganization's network in order to map a drive from a PC there to their PC here. Is this a security risk to my network, and if so to what extent? Should I allow this activity? We have a Microsoft Active Directory with CISCO pix firewall.
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Absolutely. If you don't implicitly trust (or control) the network they're linking to, then it's a risk.
Short answer:  yes

Longer answer:  Any access by any thing that is outside of your control is a security risk.  The question should be "is it a manageable risk?".  Do they have antivirus?  Is it up to date?  How do you know?  What ports are open?  When?  To who?  Why?  What level of access will they have?  To what information?  How long?  How will you track that information?  Etc, etc, etc...
It's not an unusual thing to do, however the question really is, how important is what they're doing vs the risk.. which only you can determine as you know their circumstances.

Effectively, you'll be putting their PC on your network.. and potentially linking the two networks.

You could consider removing your local PC from your network / domain whilst it's done in order to check it's clean etc afterwards.

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jimdarchAuthor Commented:
I appreciate the inclusion of a practical suggestion on how to handle the risk involved.
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