I don't have an installation of SQL CE to experiment with, but give this a try. From the quick Google results, I gather that CE has problems with subqueries that return distinct values -- the Count(*) in the code I initially offered -- but it should be OK with subqueries that return sets of results. If that's the case, try joining the base "show me the NICs" query against itself in a subquery but specifically make the link against not-the-current-NIC.
It's not elegant, but it's a starting point if it works.
Select Top 1000000
  tblAssets.AssetID,
  tblAssets.AssetName,
  tsysAssetTypes.AssetTypename,
  tsysAssetTypes.AssetTypeIcon10 As icon,
  tblAssets.Lastseen,
  tblAssets.Lasttried,
  tblNetwork.IPAddress,
  tblNetwork.Description
From
  tblAssets
  Inner Join tblAssetCustom On tblAssets.AssetID = tblAssetCustom.AssetID
  Inner Join tsysAssetTypes On tsysAssetTypes.AssetType = tblAssets.Assettype
  Inner Join tblNetwork On tblAssets.AssetID = tblNetwork.AssetID 
    And tblNetwork.IPAddress <> ''
    And tblNetwork.IPAddress <> '0.0.0.0'
    And tblNetwork.Description Not Like 'VMWare%'
    And tblNetwork.Description Not Like '%virtua%'
    And tblNetwork.Description Not Like '%Loopback%'
    And tblNetwork.Description Not Like '%USB Remote NDIS Network Device%'
  Inner Join ( SELECT
                 tblAssets.AssetID,
                 tblNetwork.IPAddress,
                 tblNetwork.Description
               FROM
                 tblAssets
                 Inner Join tblAssetCustom On tblAssets.AssetID = tblAssetCustom.AssetID
                 Inner Join tsysAssetTypes On tsysAssetTypes.AssetType = tblAssets.Assettype
                 Inner Join tblNetwork On tblAssets.AssetID = tblNetwork.AssetID 
                   And tblNetwork.IPAddress <> ''
                   And tblNetwork.IPAddress <> '0.0.0.0'
                   And tblNetwork.Description Not Like 'VMWare%'
                   And tblNetwork.Description Not Like '%virtua%'
                   And tblNetwork.Description Not Like '%Loopback%'
                   And tblNetwork.Description Not Like '%USB Remote NDIS Network Device%'
               WHERE
                 tblAssetCustom.State = 1
             ) AS SecondNIC ON SecondNIC.AssetID = tblAssets.AssetID
                               AND SecondNIC.Description <> tblNetwork.Description
                               AND SecondNIC.IPAddress <> tblNetwork.IPAddress
Where tblAssetCustom.State = 1
Order By
  tblAssets.AssetName,
  tblNetwork.Description