This is probably a Superuser question more than a Server Fault question, but I did want to make the point that a NAS running Windows XP embedded isn't, very likely, using any really old networking protocols (from a Microsoft networking perspective). Until you get back to the Windows 95/98 days (or prior), you're not going to run into really icky stuff like NetBEUI.
If the NAS is running Windows XP Embedded then it shouldn't have any problem with SMB password encryption. Not having used a lot of LaCie products I can't say for sure what the problem is you're seeing, but I sincerely doubt the LaCie is exporting any Windows file sharing protocol other than NetBIOS over TCP / SMB.
I suppose you could attempt to enable plaintext SMB authentication just to see if it fixes your problem, though. Its unclear to me whether this would work on Windows 7 or not, but you could try setting the DWORD value "EnablePlainTextPassword" to "1" at "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LanmanWorkStation\Parameters". Reboot (or stop and restart the "Workstation" service) and see what that does.
Check out Chris S comment below. It's very likely that the default LMCompatibilityLevel of Windows 7 (which is "3", meaning "Send NTLMv2 only") is causing your problem if your LaCie device is using an older SMB server (like a Samba version pre-3.0.21, for example).