Looks good: there's just one real syntactic error and one
overlooked word, though I've also suggested what I think are
likelier interpretations in a few places.

At 12:16:19 PM on Thursday, June 24, 2010, Fred and Grace
Hatton wrote:

> ... er reynði enn at hleypa undan dreka.
> ... who still tried to run away from (the) dragon.

'Escape from' probably gives a more accurate impression of
the intended sense than 'run away from'.

> En Meis mælti, "Sjá hólmganga fær eigi haldit fram,
> móðurníðingr."

> But Meis spoke, "That duel is not able to continue?,
> mother-nithing."

'Continue' is correct. <Níðingr> can be a pretty unspecific
term of extreme opprobrium, but one of its senses is
'apostate', and CV mentions that it was applicable in
particular to traitors. A <móðurníðingr> would presumably
be someone who betrayed his mother, treated her with extreme
and wanton cruelty, or the like.

> Þat er mjök fleiri menn hér, ...
> There are more men here, ...

There are many (mjök) more men here, ...

> Fær engi maðr höggvit skjótari en Meis Vindússon, ...

> No man was able more quickly to smite? than Meis Vindu's
> son ...

Yes, or 'strike'.

> ok Jóði Gormóarson sté fram, ...
> and Yoda Gormoarson stood in front ...

<Standa fram> can also mean 'to stand forth, to step forth',
a sense that fits the context here better.

> En dreki lifði enn, ok hann drap með eldi, eða með
> klóunum, eða með blóðgum tönnum, alla menn er hann fekk
> rekna:

> But (the) dragon still lived and he killed with fire or
> with claws or with bloody teeth, he was able to drive back
> all men,

This is the only real bobble: <er> is the relative particle.
I'd also translate the verb a little differently, since
<reka> can also be 'to shove violently' and 'to pound': '...
and he killed ... all the men that he could hit hard'.

> En engi maðr fekk rekinn dreka, því at skinn hans var hart
> sem steinn.

> But no man was able to drive the dragon because his skin
> was hard as stone.

<Reka> is tough to pin down. Here, considering the previous
sentence and the bit about the hardness of the dragon's
skin, it probably means that no one was able to thrust or
drive any weapon into the dragon or otherwise harm it.