It shouldn't be too hard to put something together that's in the same vein as the 4e chart. Let me see what I can do...
From the 4e Rules Compendium, pg 126:
An easy DC is a reasonable challenge for creatures that do not have training in a particular skill. Such creatures have about a 65 percent chance of meeting an easy DC of their level. An easy DC is a minimal challenge for a creature that has training in the skill, and it is almost a guaranteed success for one that also has a high bonus with teh skill...
A moderate DC is a reasonable challenge for creatures that have training in a particular skill as well as for creatures that don't have training but do have a high score (18 or higher) in the skill's key ability. Such creatures have about a 65 percent chance of meeting a moderate DC of their level...
A hard DC is a reasonable challenge for creatures that have training in a particular skill and also have a high score (18 or higher) in the skill's key ability. Such creatures have about a 65 percent chance of meeting a hard DC of their level.
I would start there, and with hard DCs (though I'd change the starting assumptions to a stat of 16 at lower levels, personally).
A 1st level 3e character with max ranks (4), a 16 stat (+3) and no other bonuses has a +7 to a skill check. If the DC is 15, this guy makes the check on a natural 8 or higher- 65% of the time.
I'd increase hard DCs at a rate just over 1 per level. Between Skill Focus or +2/+2 feats, items boosting skills, racial bonuses and ability increases from level and gear, I'd add an extra +1 to the DC something like four to eight times- maybe as often as every odd level after 1st, but I would have to look at some 3e pcs again, and it has been a while.
At the opposite (easy) end, a pc with a 10 stat and no ranks has a total of +0, which doesn't automatically go up by levels (unlike in 4e). I'd start with the same easy DC of 8 as 4e, but only increase it a bit with levels- about as often as you bump the DC on hard checks above the 1/level progression. So maybe up to DC 14 or 17 by 20th level. This is a weird case, though; 4e's assumptions on math by level are so baked in here that it's hard to say. I mean, higher level pcs will have higher stats, a smattering of ranks in barely-trained skills here and there, etc...
For moderate DCs,I'd start with the assumption of "4 ranks, no stat bonus" at first level. To make this 65% of the time, the DC should be 12. This one I'd increase slightly slower than 1/level, maybe leaving the DC stable on levels that end in 5 and 0.
What's this look like in practice?
Level --- Easy/Moderate/Hard DC
1 --- 8/12/15
2 --- 8/13/16
3 --- 8/14/17
4 --- 9/15/19
5 --- 9/15/20
6 --- 9/16/21
7 --- 10/17/23
8 --- 10/18/24
9 --- 10/19/25
10 --- 10/19/26
11 --- 11/20/28
12 --- 11/21/29
13 --- 11/22/30
14 --- 11/23/31
15 --- 12/23/33
16 --- 12/24/34
17 --- 12/25/35
18 --- 12/26/36
19 --- 13/27/38
20 --- 13/27/39
Like I said, it's been a while since I've 3e'd, but that feels about right to me. I'd have to really look over some stats to check it out, though.
