Imperial Guard

I'm worried then when i have my dark eldar, imperial guard will just eat me through sheer firepower and numbers.

How would I win against them?

Well I would think since our vehicles would go down pretty fast, should prolly take a lot of them and make use of reavers to get back armor, beast packs, wracks and grots for the high toughness and strength. Don't think I would even bother with haywired wyches, I would assume they'd probably go down pretty fast. I would give all my vehicles aethersails, and pray I get first turn. Scourges may not be a horrible option either. Although deep striking behind them may not be viable as I would assume they would have backed all there vehicles to the table edge. Use the grots to get up close quick In a raider to start busting up the tanks. The beasts to make paste of infantry and the wracks to do the same and or claim objectives. I'm not sure I would even bring ravagers, think I would just try to bring as many high toughness units I could. This all paper thoughts though, I haven't had the opportunity to play them.

Blast tempelets help dramatically from my eldar allies. Its hard man. If its DE only I think get the most lances and shots you possibly could. I haven't beat one imperial guard player yet with a only DE army. It seems like there's aren't enough shots to take out their army/troops.

Just play the game for objectives is the best I can suggest. I have beaten an army of guard and demons allies though and won against a tournament player that way but that was before the new demon army codex came out.

Imperial guard suffer well from a number of things DE can do - they're not an easy matchup, but they're certainly beatable.

Wyches with Haywires are an excellent tool versus his parking lots.
Splinter fire still mows down IG infantry blobs. (the average Venom will kill 3-4 IG a turn [depending on if they're in cover or not] which means the usual 4-6 Venoms most of our armies have can eat most IG squads alive if they're Vets, or chew a big meaty hunk out of regular troops)
Remember also, 1 on 1, Warriors are better in assault than IG as well. In fact, charging a blob with a batch of Warriors first is a great way to ensure your Wyches can charge in unopposed by overwatch to eat face.
Also remember, strike one flank of the giant sprawl of tanks and men - eat it and work your way down. You can't likely get out of the IG's range, but you *can* keep having half his army block LoS for the other half.
If he brings Air Cav stay mobile, line up on rear armor as best you're able and unleash waves of lance fire. Make sure to down something or make it a non-threat before changing targets.

http://www.thedarkcity.net/t6935-1850-all-comers

don't know how a list like this would hold up against IG/Tau.

Don't try to outshoot IG or Tau~ you'll loose. Here are my suggestions: Get close and assault them. Use night shields and flicker fields to get through turn one and assault them on turn two. Raiders full of grotesques or incubi with a pain token are pretty durable. Beast packs can be durable and fast. They'll get there turn 2. Use venom fire to get rid of units you don't want to assault (bubble wrap). A farseer is pretty helpful (use fortune if you can get it). Be careful of overkill. As always, you'll want to win the combat on your opponent's turn to avoid getting caught in the open. I hope this is helpful. RB

Actually I have had really good luck out shooting tau. Granted its at lower point games, however it's all relative. I stack up as many 3-4 man trueborn squads with 2 splinter cannons and park them in ruins or something with a decent cover and bring as many venoms with warriors as I can. I always go straight for marker lights IE pathfinders and warriors mostly. I ignore everything else until marker lights are gone. I use my reavers as harassment squads against long range shooters. I will even sacrifice them for this purpose for another uninterrupted round of shooting. Works really well for me. Also will throw in haywired wyches in a venom to scare tanks

Thanks for the Tau tips. That's all a buddy of mine is playing right now so that's what I'm dealing with.
"Take out there Marker Lights. We'll meet you in the middle. Right."

-Jack-