It depends on the codec and codec settings you choose when exporting out of VirtualDub. Lagarith RGB will give you 4:4:4, as will UT RGB. UT YUV 4:2:2 BT.709 will give you 4:2:2. Similarly, UT YUV 4:2:0 BT.709 will produce a 4:2:0 file. Lagarith YV12 is 4:2:0 and YUY2 is 4:2:2.
NB: If you are exporting a final version of your sequence (IOW, not an intermediate file that will be composited), then you don't gain anything by exporting from 4:2:0 source video to 4:2:2 or 4:4:4. The extra color information wasn't in the source, and it won't be in the export. All you'll do is waste export time and disk space.